UNIVERSITY  OF  ILLINOIS 
LIBRARY 


class 

551 


Book 


Volume 

'>vcro.^S5‘-5^ 


Mr  10-20  M 


geology 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS'  SMITH,  DIRECTOR 


BULLETINS 


Nos.  355-359 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

I SCO 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/magnesitedeposit3553hess 


CONTENTS 


Geological  Survey,  bulletin  355;  Magnesite  deposits  of  California. 
Same  356;  Geology  of  Great  Falls  coal  field,  Mont. 

Same  357;  Preliminary  report  on  Coalinga  oil  district,  Cal. 

Same  358;  Geology  of  Seward  Peninsula  tin  deposits,  Alaska. 
Same  359;  Magnetite  deposites  of  Cornwall  type  in  Pennsylvania. 


4 

169054 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  Director 


Bulletin  355 


THE 

MAGNESITE  DEPOSITS 


OF 


CALIFORNIA 


BY 

FRANK  L.  HESS 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1908 


CONTENTS. 


Page. 

General  remarks 7 

Introduction 7 

Composition,  properties,  and  uses 8 

General  character 8 

Manufacture  and  use  of  carbon  dioxide 8 

Calcination  of  magnesite 9 

Magnesia  brick,  shapes,  and  crucibles 11 

Magnesium  carbonates 13 

Oxychloride  cement 13 

Other  uses 14 

Market  for  California  magnesite , v 15 

Production 16 

Imports  of  magnesite  and  its  products 16 

Description  of  deposits 17 

General  statement 17 

The  Coast  Range  occurrences 21 

Mendocino  County 21 

Hixon  ranch  deposits 21 

Sonoma  County 1 22 

Creon  deposit 22 

Eckert  ranch  deposits 23 

George  Hall  ranch  deposit „ 24 

Pat  Cummings  claim 24 

Gilliam  Creek  deposits 24 

Madeira  deposit 25 

Unnamed  deposit 25 

Red  Slide  deposits 26 

Norton  ranch  deposits 28 

Napa  County 28 

General  remarks 28 

Walters  or  White  Rock  deposit 28 

Snowflake  and  Blanco  claims 29 

Priest  deposit 31 

Russell  deposit 31 

Matthai  deposits 31 

Santa  Clara  County 31 

Deposits  near  Coyote 31 

Bay  Cities  Water  Company’s  land 32 

Mrs.  A.  F.  Cochrane’s  land 33 

Red  Mountain  deposits . . 33 

Other  Santa  Clara  County  deposits 37 

Alameda  County 37 

King  claim 37 

Banta’s  camp  deposit ., 37 

Stanislaus  County 37 

San  Benito  County 38 


3 


4 


CONTENTS. 


Description  of  deposits — Continued. 

The  Coast  Range  occurrences — Continued.  Page. 

San  Luis  Obispo  County 38 

Santa  Barbara  County 38 

Riverside  County 38 

The  Sierra  Nevada  occurrences 39 

Kern  County 39 

Tulare  County 39 

White  River  deposits 39 

Deer  Creek  deposits 39 

Porterville  deposits 39 

Deposits  on  South  Fork  of  Tule  River 46 

Round  Valley  deposits 48 

Deposits  near  Exeter 49 

Naranjo  deposits 49 

Other  Tulare  County  deposits.. 49 

Fresno  County 50 

Mariposa  and  Tuolumne  counties 51 

Placer  County 52 

Magnesite  deposits  in  other  countries 52 

North  America 53 

Canada 53 

Quebec 53 

British  Columbia 53 

Mexico 54 

Lower  California 54 

South  America 55 

Venezuela 55 

Europe 55 

Austria 55 

Hungary 56 

Germany 56 

Greece : 57 

Italy 58 

Macedonia 58 

Norway 59 

Russia 60 

Africa 60 

Transvaal 60 

Other  African  deposits 61 

Asia 61 

India 61 

Madras 61 

Mysore 61 

Ceylon 61 

Australia 62 

Queensland 62 

New  South  Wales 62 

South  Australia 62 

Tasmania 62 

Oceania 63 

New  Caledonia 63 

Index 65 


ILLUSTRATIONS. 


Page. 


Plate  I.  Map  of  California,  showing  distribution  of  magnesite  deposits 

II.  Specimens  of  magnesite,  showing  conchoidal  fracture 8 

III.  Weathered  surfaces  of  magnesite 18 

IV.  A,  Small  irregular  vein  of  magnesite  in  serpentine;  B,  Magnesite 

weathered  under  several  inches  of  clay 20 

V.  A,  Outcrop  of  magnesite  on  Hixon  ranch,  Mendocino  County;  B, 
Entrance  to  lower  tunnel  on  Sonoma  Magnesite  Company’s  claim, 
near  Cazadero;  C,  Outcrop  of  magnesite  vein  on  Walters  claim, 

Pope  Valley 20 

VI.  Cracks  in  magnesite  apparently  due  to  shrinkage:  A,  Compact 
magnesite  from  the  Hixon  ranch,  Mendocino  County;  B , Less 
compact  magnesite  coated  with  a thin  layer  of  quartz,  also 
cracked,  from  locality  4 miles  northeast  of  Porterville 22 


VII.  Structure  of  magnesite  on  Bay  Cities  Water  Company’s  land  on 
Coyote  Creek:  A,  Specimen  from  the  upper  deposit,  showing  a 
natural  surface;  B,  Specimen  from  the  lower  deposit,  showing 


a smoothly  ground  surface 32 

VIII.  A,  Stockwork  of  magnesite  veins  miles  south  of  Winchester; 

B,  Sheeted  serpentine  containing  many  thin  veins  of  magnesite 

near  Deer  Creek,  Tulare  County 38 

IX.  A,  Amphibolite  dike  cutting  through  flat  vein  of  magnesite;  B, 

Crushed  magnesite  vein  near  Porterville, 40 

X.  Northern  hill  at  the  Willamette  Pulp  and  Paper  Company’s  mag- 
nesite mine  near  Porterville:  A,  Nearly  vertical  vein;  B,  Lower 
‘ 1 blanket  ’ ’ vein 42 

XI.  A,  Outcrop  of  stockwork  of  veins  at  north  end  of  Willamette  Pulp  and  . 

Paper  Company’s  deposits  near  Porterville;  B , Furnace  for  calcin- 
ing magnesite  at  Willamette  Pulp  and  Paper  Company’s  magnesite 
mine  near  Porterville 44 

XII.  A,  Magnesite  vein  on  south  side  of  Kings  River,  9 miles  east  of 

Sanger,  Cal. ; B,  Magnesite  vein  on  Snow  Cap  claim,  north  side  of 

Kings  River,  9 miles  east  of  Sanger 50 

Fig.  1.  Diagram  of  Western  Carbonic  Acid  Company’s  plant  at  Sedan,  Cal 9 

2.  Plan  of  magnesite  veins  and  workings  4 miles  northeast  of  Porter- 

ville, Cal 42 

3.  Diagram  showing  mode  of  working  a highly  inclined  magnesite  vein 

at  Willamette  Pulp  and  Paper  Company’s  mine  near  Porterville,  Cal . 44 

4.  Elevation  and  plan  of  Willamette  Pulp  and  Paper  Company’s  furnace, 

4 miles  northeast  of  Porterville,  Cal 45 


o 


. 


■ 


MAP  OF  CALIFORNIA,  SHOWING  DISTRIBUTION  OF  MAGNESITE  DEPOSITS  (•). 


THE  MAGNESITE  DEPOSITS  OF  CALIFORNIA, 


By  Frank  L.  Hess. 

GENERAL  REMARKS. 

INTRODUCTION. 

Magnesite,  or  magnesium  carbonate,  ordinarily  occurs  in  veins  or 
in  masses  replacing  other  rocks  rich  in  magnesia,  though  it  seems 
probable  that  a few  isolated  and  impure  deposits  in  Quebec  are  of 
sedimentary  origin.  (See  p.  53.)  Although  it  can  hardly  be  classed 
as  a common  mineral,  it  exists  in  comparatively  large  deposits  at 
many  places  in  various  parts  of  the  world.  The  principal  foreign 
deposits  now  worked  are  in  Austria,  Greece,  India,  Italy,  Norway, 
Russia,  and  South  Africa.  Other  deposits  which  are  either  not  worked 
or  from  which  the  output  is  small  occur  in  Africa,  Australia,  British 
Columbia,  Lapland,  Mexico,  Quebec,  and*  Venezuela. 

In  the  United  States  the  only  important  deposits  known  are  in 
California.  Small  veins  of  miner alogic  interest  only  have  been  noted 
in  Pennsylvania,®  Maryland,6  and  Massachusetts,0  and  veins  of 
unknown  extent  are  reported  to  exist  in  Nevada  and  Arizona. 

The  Maryland  and  Pennsylvania  deposits  were  at  one  time  worked 
in  a small  way,  the  product  being  used  for  making  Epsom  salts 
(magnesium  sulphate)  and  other  chemicals,  but  magnesite  from 
Austria,  Greece,  and  South  Africa  can  now  be  imported  so  cheaply 
that  it  no  longer  pays  to  operate  them. 

In  California  the  deposits  are  scattered  along  the  Coast  Range 
from  Mendocino  County,  and  possibly  farther  north,  to  a point  south 
of  Los  Angeles,  and  along  the  western  slope  of  the  Sierra  Nevada 
from  Placer  County  to  Kern  County.  (See  PI.  I.)  Deposits  are 
worked  in  Sonoma  County  near  Cloverdale,  in  Santa  Clara  County 
near  Livermore,  and  in  Tulare  County  near  Porterville.  Mines  were 
formerly  operated  in  Chiles  and  Pope  valleys,  Napa  County,  and 

a Frazier,  P.,  jr.,  Lancaster  County:  Second  Geol.  Survey  Pennsylvania,  Vol.  CCC,  1880,  pp.  89,  97, 

176-179,  196. 

b Bascom,  F.,  The  geology  of  the  crystalline  rocks  of  Cecil  County : Cecil  County  report,  Maryland  Geol. 
Survey,  1902,  pp.  96-97. 

c Dana,  J,  D.,  A system  of  mineralogy,  6th  ed.,  1892,  p.  275. 


7 


8 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


considerable  prospecting  and  preparatory  work  has  been  done  at 
several  other  places  with  desultory  production. 

The  field  work  on  which  the  present  article  is  based  was  done  in 
November,  1905,  and  during  the  winter  of  1906-7. 

The  literature  of  magnesite  deposits  is  scanty,  and  aside  from 
paragraphs  and  short  general  articles  appearing  in  current  periodicals 
from  time  to  time,  but  little  has  been  published  on  the  California 
magnesite  deposits. 

COMPOSITION,  PROPERTIES,  AND  USES. 

GENERAL  CHARACTER. 

Magnesite  is  a carbonate  of  magnesium  (MgC03),  having,  accord- 
ing to  Dana,a  a specific  gravity  of  3 to  3.12,  and  a hardness  of  3.5  to 
4.5.  It  is  somewhat  heavier  than  cal  cite  (2.714  specific  gravity),  and 
is  about  one-third  harder,  the  hardness  of  calcite  being  3.  It  contains 
52.4  per  cent  of  carbon  dioxide  (C03)  and  47.6  per  cent  of  magnesia 
(MgO). 

As  it  occurs  in  the  California  deposits,  magnesite  when  compara- 
tively pure  is  ordinarily  a beautiful,  white,  fine-grained  rock,  with  a 
conchoidal  fracture  that  looks  like  a break  in  china.  (See  PI.  II.) 
It  will  take  a fine  polish  and  when  so  treated  is  an  opaque  white. 
Locally  a portion  of  the  magnesite  occurs  in  a fine  powder  in  what 
seem  to  be  decomposition  cavities  and  upon  surfaces  exposed  to 
weathering. 

MANUFACTURE  AND  USE  OF  CARBON  DIOXIDE. 

Magnesite  gives  off  carbon  dioxide  on  strong  heating  and  is  used 
in  preference  to  limestone  for  the  production  of  this  gas,  as  it  contains 
a much  greater  proportion  than  calcium  carbonate,  which  carries  but 
44  per  cent.  Other  advantages  of  magnesite  are  that  the  residual 
magnesia  left  after  calcination  is  more  valuable  than  lime,  and  that 
the  amount  of  heat  required  to  drive  off  the  carbon  dioxide  is  much 
less. 

Considerable. amounts  of  liquid  carbon  dioxide  are  manufactured 
in  Oakland  from  magnesite.  As  made  at  the  Western  Carbonic  Acid 
Gas  Company’s  plant  at  Sedan  (Emeryville  post-office),  a suburb  of 
Oakland,  the  magnesite  is  fed  into  a kiln  with  about  one-tenth  its 
weight  of  coke,  and  the  gas  from  the  combustion  of  the  coke,  together 
with  that  driven  off  from  the  magnesite,  is  pumped  into  scrubbers,  of 
which  there  are  three,  filled  with  broken  limestone  to  counteract  any 
sulphuric  acid,  and  washed  with  sea  water.  The  use  of  sea  water  rather 
than  fresh  water  is  merely  an  economy.  The  gas  then  passes  to  an 
absorption  tower  where  it  comes  into  contact  with  a sprayed  solution 


a Dana,  J.  D.,  A system  of  mineralogy,  6th  ed.,  1892,  p,  274. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  II 


B 

SPECIMENS  OF  MAGNESITE  SHOWING  CONCHOIDAL  FRACTURE. 

A,  From  vicinity  of  Success  schoolhouse,  8 miles  east  of  Porterville;  B,  From  Red  Mountain,  Santa 
Clara  County.  Natural  size. 


COMPOSITION,  PROPERTIES,  AND  USES  OF  MAGNESITE. 


9 


of  potassium  carbonate,  by 
which  it  is  absorbed.  The 
‘ ‘loaded  solution  ” is  then 
pumped  into  boilers  where  it 
is  raised  to  a temperature  just 
below  the  boiling  point  of  wa- 
ter. The  solution  gives  up  its 
gas  and  is  pumped  back  to  the 
absorption  tower  for  another 
load,  while  the  gas  is  pumped 
through  cleansing  tanks  and 
cooling  pipes  to  a gasometer. 
It  is  then  liquefied  by  a three- 
step  compressor  and  run  into 
steel  cylinders,  holding  25  to 
60  pounds  each,  for  shipment. 
In  this  process  the  weight  of 
gas  obtained  is  about  50  per 
cent  of  the  weight  of  the  mag- 
nesite used.  The  accompany- 
ing diagram  (fig.  1)  will  proba- 
bly make  the  steps  clear.  The 
gas  is  shipped  throughout  the 
Pacific  coast  and  Southwest- 
ern States.  It  is  used  in  re- 
frigeration and  in  making  soda 
water  and  other  carbonated 
beverages.  The  magnesia  left 
as  a residue  is  shipped  to  paper 
mills  in  Oregon,  where  it  is 
used,  after  being  changed  to  a 
sulphite,  in  the  digestion  and 
whitening  of  wood  pulp  for  pa- 
per. This  is  the  chief  use  to 
which  California  magnesite  is 
put,  and  almost  the  entire  out- 
put of  the  Porterville  deposits 
eventually  finds  its  way  to 
these  mills. 

CALCINATION  OF  MAGNESITE. 

Among  men  engaged  in  cal- 
cining magnesite,  a difference 
of  opinion  has  existed  as  to  the 
temperature  at  which  the  car- 


10 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


bon  dioxide  can  be  driven  off.  In  recent  experiments  Otto  Brill®  has 
determined  this  point  and  made  a number  of  interesting  discoveries 
as  to  the  behavior  of  magnesite  when  heated.  His  experiments  were 
carried  on  with  small  amounts  of  carefully  prepared  and  purified  mate- 
rials, so  that  his  results  are  not  exactly  analogous  to  those  that  would  be 
obtained  by  using  the  raw  natural  material.  He  showed  that  calcium 
carbonate  (as  ordinary  limestone)  gives,  up  all  of  its  carbon  dioxide  at 
825°  C.  (1,517°  F.),  but  that  magnesium  carbonate  (magnesite) 
begins  to  give  off  carbon  dioxide  at  about  237°  C.  (465°  F.).  A cer- 
tain quantity  is  given  off  at  this  temperature,  after  which  little  or 
none  is  exhaled  until  the  magnesite  is  heated  to  250°  C.  (482°  F.), 
at  which  point  another  certain  quantity  escapes.  On  raising  the 
temperature  a third  partial  dissociation  point  is  reached  at  265°  C. 
(509°  F.).  Other  such  stages  were  marked  at  various  points,  and 
these  were  considered  to  show  the  successive  formation  and  break- 
ing up  of  various  basic  carbonates.  The  last  of  the  carbon  dioxide 
is  given  off  at  510°  C.  (950°  F.),  a temperature  much  below  that 
needed  to  calcine  limestone.  Brill’s  table  showing  the  different  car- 
bonates formed  is  given  below.  The  reduction  to  the  Fahrenheit 
measurement  of  temperature  is  added  by  the  writer  of  this  paper. 


Basic  carbonates  formed  in  burning  magnesite. 


Calcu- 

lated 

MgO. 

Obtained 

MgO. 

Dissociation  tem- 
perature. 

10MgO,9CO2 

Per  cent. 
50.64 

Per  cent. 
50.58 

°C. 

265 

°F. 

509 

9MgO,  8C02 

50. 79 

50. 98 

295 

563 

8Mg0,7C02 

51.20 

51.37 

325 

617 

7MgO,  6C02 

51.51 

• 51. 69 

340 

644 

6MgO,  5C02 

52.  36 

52. 35 

380 

716 

5MgO,  4C02 

53.  41 

53.03 

405 

761 

7MgO,  C02 

86.53 

86.  31 

510 

950 

The  temperature  at  which  magnesite  gives  up  the  last  of  its  carbon 
dioxide,  510°  C.,  is  below  a red  heat,  but  the  time  required  to  drive 
off  all  of  the  gas  is  not  stated  by  Brill,  and  this,  of  course,  would  vary 
with  the  size  of  the  material  used.  The  important  point,  however,  is 
that  at  this  temperature  all  of  the  carbon  dioxide  will  be  driven  off, 
so  that,  although  higher  heating  will  undoubtedly  remove  the  gas 
more  quickly,  because  the  heat  will  reach  the  inner  portions  of  frag- 
ments sooner,  it  ordinarily  means  a waste  of  fuel. 

After  magnesite  is  calcined  the  resultant  magnesia  takes  up  C02 
from  the  air,  again  returning  to  the  form  of  magnesite  or  magnesium 
carbonate,  but  it  does  this  so  slowly  that  it  can  not  compete  with  lime 
or  hard  plasters  in  structural  work. 

oUeber  die  Dissoziation  der  Karbonate  der  Erdalkalien  and  des  Magnesiumkarbonates:  Zeitschr. 
anorg.  Chemie,  vol.  45,  part  3,  June,  1905,  pp.  277-292. 


COMPOSITION,  PROPERTIES,  AND  USES  OF  MAGNESITE.  11 
MAGNESIA  BRICK,  SHAPES,  AND  CRUCIBLES. 

Calcined  magnesite  (magnesia)  is  used  'for  making  refractory  brick 
and  shapes  for  furnace  linings.  These  products  will  stand  exceed- 
ingly high  temperatures,  above  any  heat  that  can  be  obtained  in  re- 
generative furnaces,  so  that  they  are  much  used  for  lining  electric 
furnaces.  A considerable  number  are  also  employed  in  cement  kilns 
and  fire  boxes  for  burning  crude  oil,  uses  in  which  intense  and  long- 
continued  heat  must  be  endured.  They  are  also  exceedingly  resist- 
ant to  corrosion  by  basic  slags  and  most  molten  metals.  These 
qu  ah  ties  make  them  desirable  for  linings  in  furnaces  used  for  copper 
smelting  and  in  the  manufacture  of  basic  steel.  In  the  latter  proc- 
ess the  lime  added  to  remove  phosphorus  and  silica  attacks  clay 
or  silica  fire  brick  severely,  but  magnesia  brick  are  little  affected. 

Furnaces  built  of  magnesia  brick  or  shapes  must,  to  prevent  crack- 
ing, be  heated  evenly  and  as  gradually  as  possible,  so  that  the  inner 
ends  will  not  be  raised  to  a high  temperature  while  the  outer  portions 
are  still  cold.  The  same  care  must  be  used  in  cooling  off,  and  the 
furnace  must  lose  its  heat  gradually  and  evenly  if  the  shapes  are  to 
be  preserved.  Sometimes  considerable  trouble  is  caused  by  the  swell- 
ing of  magnesia  brick  and  shapes  on  heating  and  a corresponding 
shrinkage  on  cooling,  and  copper  converters  are  reported  to  have 
burst  from  this  cause.  This  difficulty  seems  to  be  due  largely  to 
insufficient  sintering,  for  very  strongly  sintered  brick  are  said  to  give 
little  trouble. 

A plant  for  the  manufacture  of  magnesia  brick  was  erected  at 
Clinton,  a suburb  of  Oakland,  in  1905,  and  is  still  in  operation. 
Most  of  the  magnesia  brick  made  in  this  country  are  manufactured 
from  European  magnesite.  Some  magnesia  brick  of  foreign  manu- 
facture were  formerly  imported  each  year,  but  none  are  shown  in  the 
customs  returns  for  1907. 

Magnesia  crucibles  are  made  of  various  forms  and  different  de- 
grees of  fineness.  Crucibles  made  from  pure  magnesia  have  much 
the  appearance  of  fine  biscuit  ware.  If  heated  to  incipient  melting 
they  have  the  appearance  of  translucent  glass.  When  the  ordinary 
European  commercial  calcined  magnesite  is  used  for  crucibles,  it  has 
little  strength  above  a red  heat,  but  crushes  in  the  tongs  like  so  much 
putty.®  Dr.  Oliver  P.  Watts,  in  a long  series  of  experiments  in  the 
preparation  of  metallic  alloys,  used  magnesia  crucibles  as  finings  for 
carbon  or  graphite  crucibles  to  prevent  the  absorption  of  carbon  by 
the  charge,  and  found  that  they  answered  the  purpose  excellently. 
In  such  crucibles  alloys  of  iron  with  aluminum,  cobalt,  chromium, 
copper,  manganese,  molybdenum,  nickel,  silicon,  silver,  tin,  titanium, 


o Watts,  Oliver  P.,  in  letter  to  author. 


12 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


and  tungsten  were  made.  Chromium,  silicon,  and  titanium,  when 
forming  10  per  cent  or  more  of  the  charge,  seemed  to  attack  the 
linings,  to  judge  from  the  failure  of  a number  of  them. 

11  These  linings  are  extremely  refractory,  so  that  the  maximum 
temperature  at  which  they  can  be  used  is  fixed  not  by  their  melting, 
but  by  another  phenomenon,  the  reduction  of  the  magnesia  by  car- 
bon.”® The  carbon  attacks  the  magnesia  and  corrodes  it,  especially 
if  iron  oxide  be  present,  in  which  case,  under  very  high  temperatures, 
the  iron  oxide  is  volatilized  and,  coming  into  contact  with  the  graph- 
ite crucible,  is  reduced  and  collects  as  microscopic  spheres  of  iron. 
These  grow  and  roll  down  the  sides,  carrying  absorbed  graphite, 
which  vigorously  attacks  the  magnesia  after  the  equation  MgO  + C = 
Mg  + CO.  At  a lower  temperature  this  action  is  reversed,  and  for 
this  reason  magnesium  can  not  be  obtained  from  magnesia  by  reduc- 
tion with  carbon. 

Magnesia  crucibles  made  under  such  temperatures  are  white,  even 
when  much  iron  oxide  is  present  in  the  raw  materials,  for  the  iron 
oxide  is  volatilized  and  driven  out.6  Mr.  A.  J.  Fitzgerald,  of  Fitz- 
gerald & Bennie,  Niagara  Falls,  N.  Y.,  states  in  a letter  of  March  21, 
1908,  to  the  writer,  that  his  firm  melts  charges  of  6 or  7 pounds  of 
alloys  in  magnesia  crucibles  in  electric  furnaces  by  withdrawing  the 
charge  through  the  bottom.  Cracking  from  change  of  temperature 
is  not  likely  to  take  place  in  small,  well-fused  magnesia  crucibles. 

Much  mystery  has  been  attached  to  the  binders  used  in  making 
magnesia  brick,  shapes,  and  crucibles,  to  cement  the  particles 
together  when  burned.  It  is  a common  belief  among  persons  handling 
magnesite  that  to  make  brick  which  will  hold  together  when  burned 
it  is  necessary  to  use  magnesite  containing  impurities  consisting  of 
iron  oxides  or  serpentine.  It  is  undoubtedly  true  that  such  impurities 
will  allow  the  sintering  of  brick  at  very  much  lower  temperatures  than 
are  necessary  with  pure  magnesite,  but  they  also  make  the  brick 
more  fusible  and  more  easily  corroded  by  molten  materials.  A pure 
magnesia  brick  demands  a very  high  temperature  for  sintering,  but 
bricks  can  be  made  without  the  impurities  mentioned  or  others,  and 
when  so  made  are  extremely  refractory.  Dead-burned  magnesite — 
that  is,  magnesite  from  which  the  C02  has  been  entirely  driven  off — 
has  little  or  no  plasticity,  so  that  it  is  hard  to  handle.  It  is  said 
that  its  plasticity  is  much  improved  by  using  partly  calcined  or  caus- 
tic magnesite  with  it.  Heavy  pressure  will  bind  the  material  suffi- 
ciently to  allow  it  to  be  sintered;  240  tons  per  brick  is  used  in  the 
works  at  Snarum,  Norway.0 

a Letter  cited.  See  also  paper  by  Doctor  Watts,  The  action  of  carbon  on  magnesia  at  high  tempera- 
tures; Trans.  Am.  Electrochem.  Soc.,  vol.  10,  1907,  pp.  279-289. 

i>  Watts,  O.  P.,  op.  cit.,  p.  287. 

c Daumann,  E.,  Magnesit  fran  Snarum:  Bihang  till  Jem-Kontorets  Annaler  for  1905,  Stockholm, 
1905,  pp.  222-225. 


COMPOSITION,  PROPERTIES,  AND  USES  OF  MAGNESITE.  13 

Magnesia  may  be  melted  to  a glassy  substance  in  an  electric  furnace, 
but  when  so  treated  contains  many  bubbles.  It  seems  highly  prob- 
able that  it  would  be  profitable  to  sinter  magnesia  brick  and  similar 
products  in  an  electric  furnace,  where  electric  power  is  as  plentiful 
as  it  is  in  California. 

MAGNESIUM  CARBONATES. 

For  some  of  the  purposes  to  which  magnesite  is  rather  extensively 
put,  dolomite,  the  calcium  magnesium  carbonate,  may  be  used,  as  in 
the  making  of  magnesia  alba  levis  (light  magnesium  carbonate)  and 
Epsom  salts.  The  light  carbonate  is  well  known  as  a toilet  prepara- 
tion and  is  also  used  in  medicine.  Mixed  with  various  amounts  of 
asbestos  it  is  used  for  pipe  covering  and  boiler  lagging;  85  per  cent 
of  light  carbonate  to  15  per  cent  of  asbestos  is  a common  proportion. 
The  asbestos  is  needed  to  hold  the  powdery  carbonate  together.  For 
this  purpose  water  glass  (sodium  silicate)  is  also  sometimes  added  to 
the  mixture.  The  heavy  carbonate  is  sometimes  used  instead  of 
the  light  carbonate,  in  which  case  the  efficiency  of  the  covering 
is  probably  diminished  owing  to  the  lesser  degree  of  porosity.  The 
light  carbonate  is  said  to  make  an  excellent  absorbent  for  dyna- 
mite manufacture,  as  it  does  not  readily  allow  the  nitroglycerine  to 
“ sweat”  out.  Powdered  magnesite  is  introduced  to  prevent  scale  in 
boilers  in  which  sulphurous  waters  are  used,  as  the  magnesium  sul- 
phate (Epsom  salts)  formed  is  highly  soluble. 

OXYCHLORIDE  CEMENT. 

For  many  years  it  has  been  well  known  that  a moistened  mixture 
of  magnesium  oxide  (magnesia)  and  magnesium  chloride  will  form  an 
exceedingly  strong  cement,  and  numerous  attempts  have  been  made 
to  use  it  in  manufacturing  tiles,  artificial  stone,  flooring,  wainscoting, 
etc.  Many  of  these  attempts  have  met  with  failure  owing  to  an 
unlooked-for  decomposition  of  the  manufactured  product,  and  this 
has  prevented  the  industry  from  becoming  important  as  quickly  as 
had  been  expected.  The  failure  of  the  cement  seems  to  be  due  to 
the  presence  of  lime  either  in  the  magnesium  chloride  or  in  the  mag- 
nesia, which  in  the  form  of  chloride  is  hygroscopic  and  by  taking  up 
water  swells  and  destroys  the  usefulness  of  the  material,  and  so  where 
magnesite  is  to  be  used  in  the  manufacture  of  cement  efforts  are  made 
to  obtain  it  as  free  from  lime  as  possible. 

At  the  Malelane  deposits,  South  Africa,  the  magnesite  is  calcined,, 
ground,  and  mixed  with  imported  German  magnesium  chloride  at  the 
mine  and  shipped  ready  for  use  as  cement.® 

In  using  the  cement  for  flooring,  wainscoting,  etc.,  it  is  mixed  with 
sawdust  or  sand  and  coloring  matter  to  give  it  the  desired  tint.  It 


° Hall,  A.  L.,  The  magnesite  deposits  of  Malelane:  Rept.  Geol.  Survey,  Transvaal  Mines  Dept.,  1906, 
Pretoria,  1907,  pp.  127-132, 


14 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


may  be  laid  in  a continuous  sheet  over  considerable  areas  and  is 
said  to  crack  much  less  easily  than  cement.  The  use  of  sawdust- 
makes  the  material  very  much  lighter  in  weight  than  cement,  less 
hard,  and  more  resilient.  The  surface  is  commonly  waxed  and 
polished,  like  a wooden  floor.  At  the  present  time  a large  part  of  the 
Grecian  magnesite  imported  into  this  country  is  used  for  making  such 
floors.  The  material  has  also  been  used  for  wall  plaster,  and  in  speci- 
mens seen  by  the  writer  would  stand  severe  abuse  without  breaking. 

In  these  preparations  the  sawdust  particles  are  well  separated,  so 
that  the  material  is  in  a high  degree  fireproof.  The  same  mixture  is 
used  for  making  stationary  washtubs  and  for  similar  purposes. 

OTHER  USES. 

Sintered  magnesite  tubing  of  assorted  sizes,  up  to  31.5  inches  in 
length  and  2.8  inches  in  diameter,  is  regularly  made  for  chemical  and 
electrometallurgical  work. 

The  fusing  point  of  magnesia  has  been  determined  by  Goodwin  and 
Mailey®  as  about  1910°  C.  The  same  experimenters  found  that  the 
fused  material  is  not  acted  upon  by  fused  silver,  sodium,  potassium, 
or  barium  nitrates ; nor  by  sodium,  potassium,  or  zinc  chlorides,  bro- 
mides, or  sulphate,  even  after  an  hour’s  exposure  of  a polished  surface 
to  their  action.  Barium  chloride  has  a very  slight  action  on  it,  but 
sodium  carbonate,  potassium  sodium  carbonate,  potassium  hydrate, 
and  cryolite  attacked  the  fused  oxide  energetically.  Cold  dilute  hydro- 
chloric, nitric,  and  sulphuric  acids  attack  the  fused  oxide  slowly,  and 
concentrated  acids  are  less  active  than  dilute  acids. b The  fused  mag- 
nesite takes  up  but  little  C02  from  the  air,  and  it  is  possible  that  if 
pure  material  were  used  it  would  be  found  that  there  is  no  recombi- 
nation with  carbon  dioxide.  In  experiments  performed  by  Fitz- 
gerald & Bennie,0  during  which  they  found  specimens  to  take  up 
0.42  and  0.63  per  cent  C02,  the  magnesia  used  contained  1.10  and 
2.48  per  cent  of  lime,  respectively,  which  may  have  been  the  com- 
bining substance.  According  to  the  experiments  of  Goodwin  and 
Mailey  the  coefficient  of  linear  expansion  of  fused  magnesia  is  almost 
the  same  as  that  of  platinum,  and  but  little  more  than  that  of  quartz 
parallel  to  the  optic  axis.  They  find  the  coefficient  of  linear  expan- 
sion between  120°  and  270°  C.  to  be— 

at=  10"8  [1140  + 0.92  (*-120°)], 
while  for  platinum  they  quote  Holborn  and  Day  as  giving — 
at=  (8889 + 1.274  t)  10'9  for  * = 0°  to  1000°. 

a Physical  properties  of  fused  magnesium  oxide:  Trans.  Am.  Electrochem.  Soc.,  vol.  9, 1906,  pp.  92-93. 

b Op.  cit.,  p.  98. 

c Discussion  of  “Physical  properties  of  fused  magnesium  oxide:”  Trans.  Am.  Electrochem.  Soc. 
vol.  9,  1906,  pp.  101-103, 


MARKET  FOR  CALIFORNIA  MAGNESITE. 


15 


In  these  formulae  at  stands  for  the  coefficient  of  expansion  at  any 
given  temperature,  t standing  for  temperature. 

A coating  of  crushed  magnesite  is  laid  on  hearths  used  for  heating 
steel  stock  for  rolling,  to  prevent  the  scale  formed  from  attacking  the 
fire  brick  of  the  hearth. 

When  heated  to  a high  degree  magnesia  becomes  incandescent  like 
lime  and  the  rare-earth  oxides.  On  account  of  this  property  numer- 
ous efforts  have  been  made  to  construct  an  incandescent  lamp,  similar 
to  the  Nernst  lamp,  which  uses  a glower  made  of  zirconia  and  yttria, 
but  not  much  success  has  been  attained.  A patent®  has  been  taken 
out  for  the  construction  of  electrodes  for  arc  lamps  from  a mixture 
containing  90  per  cent  of  magnesia  and  10  per  cent  of  iron  oxide. 
Magnesia  is  a poor  conductor  of  electricity, 6 and  the  iron  oxide  is 
introduced  to  increase  the  conductivity.  Owing  to  its  nonconduc- 
tivity magnesite  mixed  with  iron  dust  has  been  used  for  the  manu- 
facture of  rheostats. c 

Magnesia  has  been  used  for  an  adulterant  in  paint,  but  it  has  little 
virtue  as  a pigment.  Its  covering  properties  are  poor,  and  it  settles 
badly  in  the  mixture. 

Magnesium  (metal)  is  not  obtained  from  magnesite,  but  from  mag- 
nesium chloride,  which  is  obtained  in  large  quantities  from  the  Stass- 
furt  salt  deposits  in  Germany  and  from  sea  water  at  other  places. 

MARKET  FOR  CALIFORNIA  MAGNESITE. 

The  market  for  California  magnesite  is  at  present  limited  to  the 
Pacific  coast  and  Rocky  Mountain  States,  as  the  necessarily  high 
freight  rates,  due  to  the  long  railroad  haul  to  the  eastern  portion  of 
the  country,  preclude  its  shipment  in  competition  with  imported 
magnesite.  Moreover,  the  California  deposits  are  handicapped  in  the 
competition  with  foreign  deposits  by  the  much  higher  scale  of  wages 
paid  in  this  country.  Day  laborers  in  California  receive  $1.50  to  $2 
for  a ten-hour  day,  and  if  miners  are  hired  for  the  work,  $2.50  to  $3 
must  be  paid.  In  Hungary  the  wages  paid  in  1906  at  the  works  of 
the  Magnesite  Company  (Limited)  were  40  cents  per  ten-hour  day  for 
common  labor  and  80  cents  for  foremen.**  Besides  these  drawbacks, 
none  of  the  California  veins  compare  well  in  size  with  the  reported 
width  of  the  Hungarian  veins.  In  quality,  however,  the  comparison 
with  the  foreign  material  is  favorable;  in  fact,  the  California  article 
is  ordinarily  better. 

Magnesite  from  Porterville  now  costs  about  $6.50  per  short  ton 
laid  down  at  San  Francisco;  probably  that  from  the  Gilliam  Creek 
(Sonoma  County)  deposits  can  be  delivered  for  somewhat  less.  Pro- 

a Lewis  J.  Jones,  letters  patent  No.  484553,  dated  October,  1892. 

b The  conductivity  of  magnesia  when  heated  is  treated  in  the  article  by  Goodwin  and  Mailey,  to  which 
reference  has  been  made  (p.  14). 

c E.  W.  Gilbert,  letters  patent  No.  439939,  dated  November  4,  1890. 

Private  letter. 


16 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


duction  at  the  Kings  River  deposits  will  cost  about  the  same  as  at 
Porterville.  Magnesite  from  Sonoma  and  Napa  counties  can  prob- 
ably be  calcined  and  laid  down  in  San  Francisco  at  $15  per  short  ton. 
Imported  magnesite  is  now  (April,  1908)  quoted  in  New  York  City 
at  $7.25  to  $8  per  long  ton,  equal  to  $6.38  to  $7.08  per  short  ton; 
calcined  magnesite  is  quoted  at  $16.75  to  $25,  and  when  compara- 
tively free  from  lime,  ground,  sells  in  small  lots  at  the  latter  price. 
With  this  difference  in  price  for  calcined  magnesite  of  about  $5  to  $6 
between  San  Francisco  and  New  York,  it  seems  possible  that  this 
product  could  sometimes  be  shipped  at  a profit  to  the  eastern  coast 
of  the  United  States  on  vessels  that  would  otherwise  sail  without  a 
full  cargo  and  would  for  this  reason  be  willing  to  carry  the  material 
at  low  rates. 

In  spite  of  the  fact  that  the  California  magnesite  is  ordinarily  purer 
and  cheaper,  calcined  Grecian  magnesite  is  shipped  into  Los  Angeles 
as  “ white  cement”  for  use  in  oxychloride  cement. 

PRODUCTION. 

The  production  of  magnesite  in  California  since  1891,  the  first  date 
for  which  figures  are  available,  has  been  as  follows : 

Quantity  and  value  of  crude  magnesite  produced  in  California , 1891-1907. a 


Short 

tons. 

Value. 

Short 

tons. 

Value. 

1891 

439 

1,004 

704 

1,440 

2,220 

1,500 

1,143 

1,263 

1,280 

$4,390 

10,040 

7,040 

10,240 

17.000 

11.000 
13, 671 
19,075 
18,  480 

1900 

2,252 
3,500 
2,830 
3, 744 
2,850 
3,933 
7,805 
b 7,  762 

$19, 333 
10, 500 
8,490 
10,595 
9, 298 
15, 221 
23, 415 
50, 453 

1892 

1901 

1893 

1902 

1894 

1903 

1895 

1904 

1896 

1905 

1897  . 

1906 

1898  . 

1907 

1899 

a Yale,  C.  G.,  Magnesite:  Mineral  Resources  U S.  for  1906,  U.  S.  Geol.  Survey,  1907.  The  figures  for 
1907  were  also  kindly  furnished  by  Mr.  Yale 
b From  this  amount  3,234  tons  of  calcined  magnesite,  worth  $20  per  ton,  was  produced. 


IMPORTS  OF  MAGNESITE  AND  ITS  PRODUCTS. 

The  imports  of  magnesite  into  the  United  States  for  the  last  three 
years  have  been  as  follows : 

Imports  of  magnesite  and  magnesite  products  into  the  United  States  in  1905,  1906,  and 

1907. a 


1905. 

1906. 

1907. 

Pounds. 

Value. 

Pounds. 

Value. 

Pounds. 

Value. 

Magnesia: 

Calcined,  medicinal 

Carbonate  of,  medicinal . . 
Sulphate  of,  or  Epsom 

salts 

Magnesite: 

Calcined,  not  purified 

Crude 

13, 554 
21, 901 

9,039,099 

134,595,334 
14, 152, 466 

$2, 778 
1,360 

38,084 

575,355 

63,264 

30, 788 
39, 487 

5,830,224 

141,314,682 
39, 477, 766 

$5, 689 
5,844 

22, 471 

740,585 

122,908 

49,489 
85, 467 

4,532, 713 

151, 137, 661 
46,878, 740 

$9,005 

3,994 

16,256 

688,371 

186,988 

a Figures  furnished  by  Bureau  of  Statistics. 


GENERAL  DESCRIPTION. 


17 


There  is  no  duty  on  magnesite  or  calcined  magnesite,  nor  on  the 
salts  of  magnesium  mentioned  in  the  table.  For  some  reason  the  cal- 
cined magnesite  imported  in  1907  is  declared  of  much  lower  value  than 
the  market  price  ($8.11  per  ton  as  compared  with  $16.75  to  $25). 

DESCRIPTION  OF  DEPOSITS. 

GENERAL  STATEMENT. 

The  California  magnesite  deposits,  so  far  as  known,  all  occur  as 
veins  in  connection  with  serpentinized  magnesian  rocks.  By  far  the 
larger  part  are  in  the  Coast  Range,  in  the  serpentinized  rocks  that 
stretch  from  southern  California  into  Oregon.  These  rocks,  although 
in  few  places  wholly  altered,  will  be  referred  to  as  serpentines,  the 
name  by  which  they  are  ordinarily  known.  Those  in  the  Coast  Range 
are  probably  lower  Cretaceous  in  age  a and  cover  large  areas,  Becker  6 
estimating  that  between  Clear  Lake  and  New  Idria,  a distance  of 
about  200  miles,  there  are  more  than  1,000  square  miles  of  serpentine. 
Through  a large  part  of  this  area  magnesite  veins  of  various  sizes  are 
found.  Veins  large  enough  to  be  more  or  less  workable  are  known  to 
occur  at  many  places  in  Mendocino,  Sonoma,  Napa,  Alameda,  Stan- 
islaus, and  Santa  Clara  counties.  Along  the  western  side  of  the 
Sierra  Nevada  magnesite  is  found  in  Placer,  Fresno,  Tulare,  and 
Kern  counties,  and  in  southern  California  in  Riverside  County. 

The  serpentines  of  the  Coast  Range  are  ordinarily  greenish  or  bluish, 
greatly  broken  and  faulted,  a solid  block  a foot  in  diameter  being  a 
rarity  in  many  localities.  They  are  derived  from  olivine-pyroxene 
rocks,  in  which  the  amounts  of  the  minerals  vary  in  ratio  at  different 
localities.  Here  and  there  the  rocks  still  carry  considerable  portions 
of  only  partly  altered  minerals,  though  the  general  decay  is  far 
advanced.  There  is  great  difference,  both  in  the  comparative  amounts 
of  the  original  minerals  from  which  the  serpentine  is  formed,  and  in 
the  degree  of  serpen tinization,  even  in  small  areas.  Some  rocks  are 
almost  wholly  made  up  of  partially  serpentinized  olivine,  in  places 
carrying  chromite  and  chromic  mica,  while  near  at  hand  other  speci- 
mens show  large  quantities  of  orthorhombic  pyroxene.  Along  the 
Sierra  Nevada  the  serpentine  at  the  Fresno  and  Tulare  County  locali- 
ties is  of  a dull  drab  or  brown  color  and  that  in  Tulare  County  is  much 
less  broken  than  the  Coast  Range  serpentines. 

Magnesite  is  probably  formed  both  from  the  breaking  down  of  the 
serpentine-making  minerals  and  from  the  serpentine  itself.  In  a 
specimen  from  the  northeast  corner  of  Santa  Clara  County  ensta.tite 
has  been  replaced  by  magnesite.  Many  of  the  cracks  in  the  olivine 
are  filled  by  magnesite.  These  cases  seem  to  show  the  derivation  of 

a Fairbanks,  H.  W.,  San  Luis  folio  (No.  101),  Geologic  Atlas  U.  S.,  U.  S.  Geol.  Survey,  1904,  p.  6. 
b Becker,  G.  F.,  Geology  of  the  quicksilver  deposits  of  the  Pacific  slope:  Mon.  U.  S.  Geol.  Survey,  vol. 
13, 1888,  p.  103. 

51136— Bull.  355—08 2 


18 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


magnesite  directly  from  the  original  minerals,  but  the  ordinary  ten- 
dency shown  by  magnesite  bodies  is  to  occur  in  only  those  portions  of 
the  serpentine  which  show  great  decay,  the  magnesite  being  probably 
formed  mostly  from  the  serpentine. 

Van  Hisea  supposes  that  in  the  decay  of  olivine  a third  of  the  mag- 
nesium may  pass  into  magnesite,  in  which  case  he  would  write  the 
reaction  for  olivine  containing  magnesium  and  iron  in  the  atomic 
ratio  of  3:1  as  follows: 

3Mg3F  eSi208+ 3C024“  4H204"  O =2H4Mg3Si2094“  F 63044"  3MgC03-l“  2Si024"  k. 

Olivine  Carbon  Water  Oxy-  Serpentine  Magne-  Magnesite  Quartz  Heat 

dioxide  gen  tite 

Here.“k”  signifies  that  heat  is  liberated. 

This  equation  is  largely  theoretical,  and  as  a matter  of  fact  little 
magnetite  is  found  in  many  of  the  specimens  examined.  Hydrated 
oxides  of  iron  are  common,  however,  and  it  seems  probable  that  to 
such  an  equation  water  should  be  added  to  the  unknown  amount 
necessary  to  hydrate  the  iron.  At  the  same  time  it  is  to  be  remem- 
bered that  vastly  more  carbonated  water  is  ordinarily  present  than  is 
required  to  supply  the  amount  demanded  by  the  equation,  so  that  it 
seems  possible  that  under  certain  conditions,  with  this  excess  of 
carbon  dioxide  at  hand,  the  entire  amount  of  magnesium  contained 
in  olivine  carrying  equal  numbers  of  magnesium  and  iron  atoms 
may  pass  into  magnesite.  Such  a change  may  be  represented  by 
this  equation: 

4Mg2Fe2Si208+6H20+8C02+40=2(2Fe203.3H20)4-8MgC034-BSi02. 

Olivine  Water  Carbon  Oxy-  Limonite  Magnesite  Quartz 

dioxide  gen 

Enstatite  also  alters  to  magnesite,  and  in  a few  specimens  is  wholly 
replaced  by  it.  Probably  other  pyroxenes  also  form  magnesite  on 
weathering. 

It  seems  probable  that  as  a rule  both  serpentine  and  magnesite  are 
formed  in  the  process  of  decay  of  the  original  minerals  in  peridotites 
and  allied  basic  rocks,  and  that  during  the  decay  of  the  serpentine  the 
formation  of  magnesite  is  continued.  In  any  case  the  magnesia  or 
magnesian  mineral  is  changed  to  the  carbonate,  dissolved  by  perco- 
lating water  charged  with  carbon  dioxide,  and  precipitated  in  cracks 
and  crevices  as  veins.  The  silica  is  carried  away  in  solution  by  the 
water  and  is  often  deposited  in  other  veins  or  with  the  magnesite 
veins  as  opal  or  quartz. 

Many  magnesite  veins  stand  out  prominently  from  the  surrounding 
serpentine,  as  they  weather  less  readily  than  the  serpentine,  and  also 
because  in  the  vicinity  of  a magnesite  vein  the  surrounding  serpentine 
is  generally  much  decomposed  and  therefore  erodes  rather  easily. 
The  boldness  of  outcrop  and  the  snowy  whiteness  of  the  veins  form  a 


a Van  Hise,  C.  R.,  A treatise  on  metamorphism:  Mon.  U.  S.  Geol.  Survey,  vol.  47,  1904,  p.  309. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  Ill 


WEATHERED  SURFACES  OF  MAGNESITE. 

A,  From  Red  Mountain,  Santa  Clara  County;  R,  C,  From  locality  4 miles  northeast  of 
Porterville.  All  natural  size. 


GENERAL  DESCRIPTION. 


19 


strong  contrast  with  the  dull-colorecl  surroundings,  so  that  their 
occurrence  at  once  attracts  the  eye. 

Surfaces  of  comparatively  pure,  even-grained  magnesite,  exposed  to 
the  weather,  are  in  many  places  fluted  by  the  rain,  similarly  to  lime- 
stone under  like  conditions,  but  the  flutings  or  channels  are  much 
narrower.  Other  surfaces  are  covered  with  sharp-angled  irregular 
projections,  due  probably  to  impurities.  (See  PI.  III.)  At  Red 
Mountain,  Santa  Clara  County,  earth-covered  pieces  attacked  by  per- 
colating water  have  weathered  into  designs  resembling  mud  cracks, 
with  the  spaces  between  the  cracks  convex  and  a little  over  half  an 
inch  across.  (See  PI.  IV,  B.) 

In  many  of  the  larger  veins  there  is  a central  portion  of  compara- 
tively pure  magnesite,  and  in  the  same  veins  on  one  or  both  sides  there 
may  be  many  inclusions  of  serpentine.  This  mixed  condition  of  the 
magnesite  and  serpentine  is  common  in  the  large  veins  seen  along  the 
Coast  Range.  Small  inclusions  of  serpentine  in  many  places  extend 
well  into  the  vein.  Toward  the  side  the  inclusions  form  a gradually 
larger  proportion  of  the  mass  until  the  magnesite  appears  only  as  a 
great  number  of  small  veins  in  the  broken  serpentine.  Or,  if  the  main 
mass  is  approached  from  the  side,  as  along  a tunnel,  a stockwork  of 
small  veins  first  appears,  growing  thicker  toward  the  large  vein,  until 
the  larger  part  of  the  mass  is  magnesite  and  the  pieces  of  the  ser- 
pentine are  so  separated  as  to  become  inclusions  in  the  magnesite. 
This  may  result  from  two  forms  of  growth.  If  any  particular  group 
of  anastomosing  veins  grows  greatly,  the  fragments  between  the  veins 
become  so  separated  that  they  lose  their  predominance  as  compared 
with  the  magnesite,  and  the  magnesite  forms  the  greater  part  of  the 
mass.  In  the  other  form  of  growth  the  serpentine  fragments  may  be 
partly  or  wholly  replaced  by  magnesite.  Still  other  large  veins  and 
masses  are  clear  magnesite  from  the  center  to  one  or  both  sides,  either 
of  which  may  be  formed  by  much  slickensided  faults. 

There  is  considerable  difference  in  the  purity  of  the  veins  at  different 
places.  Some  are  beautifully  white  and  contain  but  a small  percent- 
age of  foreign  matter;  others  contain  iron  oxides,  silica,  clay,  or 
serpentine  in  varying  amounts  and  proportions. 

Near  the  veins  the  serpentine  has  almost  without  exception  lost  its 
normal  color  and  is  badly  rotted  and  porous  as  the  result  of  its  decom- 
position by  percolating  surface  waters.  The  rock  shrinks  through  the 
gradual  removal  of  its  components  and  the  magnesite  fills  the  enlarging 
spaces  between  the  fragments.  The  magnesite  produced  through  the 
decomposition  of  serpentine  occupies  about  four-fifths  of  the  space  of 
the  original  rock,  so  that  a magnesite  vein  may  be  and  probably  is 
formed  very  largely  from  the  serpentine  which  formerly  occupied  the 
space  now  filled  by  the  vein,  the  remainder  coming  from  the  rock  in  a 
comparatively  narrow  zone  on  each  side.  The  large  width  of  some  of 
the  veins  may  thus  be  explained,  by  supposing  that  they  occupy  the 


20 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


spaces  made  by  the  disintegration  of  the  serpentine  almost  as  fast  as 
they  are  left,  rather  than  natural  fissures  or  cracks  in  the  rocks.  The 
veins  are  thus,  in  a sense,  partly  residual  from  the  serpentine.  In 
specimens  collected  fragments  of  serpentine  are  to  be  seen  in  various 
stages  of  decomposition  and  replacement;  in  others  the  fragments  are 
as  sharp  angled  as  if  freshly  broken.  Belts  of  disintegration  naturally 
occur  along  the  channels  with  greatest  circulation  of  water,  generally 
coincident  with  the  larger  faults.  Every  crack  and  joint  along  the 
line  makes  a feeder  for  the  trunk  channels.  Among  these  reticula- 
tions the  same  process  of  decomposition  is  going  on,  and  in  places 
abrupt  enlargements  of  the  veins  occur,  making  so-called  “ bowlders” 
of  magnesite,  which  may  be  2 or  3 feet  or  even  more  in  diameter  and 
nearly  equi dimensional.  The  formation  of  such  a deposit,  on  a small 
scale,  is  shown  in  PL  IV,  A.  This  lack  of  linear  extension  in  the 
small  deposits,  together  with  the  number  of  faults  known  to  cut  the 
Coast  Range  serpentines  in  every  direction,  makes  the  following  of 
veins  by  widely  separated  outcrops  very  uncertain,  as  the  outcrops 
may  be,  and  many  of  them  are,  distinct  deposits,  though  they  happen 
to  have  a certain  alignment.  Abrupt  terminations  are  known  to 
- occur  in  the  large  deposits  as  in  the  smaller  ones,  and  it  is  unsafe  to 
expect  the  same  continuity  as  would  be  thought  probable  in  a quartz 
vein  of  equal  width. 

Two  modes  of  precipitation  of  magnesite  from  solution  suggest 
themselves.  Brucite  (Mg(H20)2),  formed  through  the  decomposition 
of  magnesian  minerals  without  carbonation,  may  take  the  C02  from 
carbonated  water  carrying  magnesite  and  thus  precipitate  both  the 
newly  formed  molecule  and  the  magnesite  carried  in  solution,  owing 
to  the  loss  of  excess  C02  in  the  water;  or  magnesite  may  be  precipi- 
tated from  carbonated  water  owing  to  the  loss  of  C02  through  evapo- 
ration. Nothing  resembling  brucite  has  been  seen,  either  in  micro- 
scopic sections  or  in  hand  specimens,  so  that  the  latter  hypothesis 
seems  more  likely,  though  possibly  it  applies  only  to  the  veins  depos- 
ited in  more  open  places,  the  former  process  going  on  in  the  small 
threadlike  veins. 

Little  is  known  of  the  depth  to  which  the  veins  extend.  If  they  are 
formed  through  the  agency  of  percolating  surface  water,  which  seems 
most  likely,  the  manner  of  precipitation  probably  has  little  to  do  with 
the  depth  to  which  they  extend  It  seems  fair  to  assume  that  the 
deposits  may  be  found  down  to  the  limit  of  easy  circulation  of  these 
waters,  a depth  of  several  hundred  feet  in  favorable  localities,  their 
size  being  modified  by  the  time  through  which  such  circulation  has 
existed,  by  differences  in  the  hardness  or  composition  of  the  rock,  etc. 
Faulting  is  as  likely  to  cut  the  veins  off  in  depth  as  in  length. 

Cinnabar  and  chromite  occur  in  the  serpentines  in  the  neighborhood 
of  many  of  the  magnesite  deposits. 


U.  3.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  IV 


A.  SMALL  IRREGULAR  VEIN  OF  MAGNESITE  IN 
SERPENTINE. 

From  Red  Mountain,  Santa  Clara  County. 


B.  MAGNESITE  WEATHERED  UNDER  SEVERAL  INCHES  OF  CLAY. 
The  surface  is  soft.  From  Red  Mountain,  Santa  Clara  County. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  V 


A.  OUTCROP  OF  MAGNESITE  ON  HIXON  RANCH,  MENDOCINO  COUNTY. 


B.  ENTRANCE  TO  LOWER  TUNNEL  ON  SONOMA  MAGNESITE  COMPANY’S  CLAIM, 
NEAR  CAZADERO. 


C.  OUTCROP  OF  MAGNESITE  VEIN  ON  WALTERS  CLAIM,  POPE  VALLEY. 
The  face  exposed  is  about  6 feet  high. 


MENDOCINO  COUNTY. 


21 


THE  COAST  RANGE  OCCURRENCES. 

The  individual  California  deposits  will  be  treated  by  counties, 
beginning  with  the  northernmost  in  the  Coast  Range  and  going 
southward  to  southern  California,  then  northward  along  the  Sierra 
Nevada. 

MENDOCINO  COUNTY. 

Hixon  ranch  deposits. — On  the  Hixon  ranch,  on  the  east  side  of 
Russian  River,  12  miles  north  of  Cloverdale,  there  are  a number  of 
outcrops  of  magnesite,  about  600  feet  (barometric  measurement) 
above  the  river,  near  the  crest  of  a long  ridge  whose  east  side  slopes 
steeply  to  a deep  canyon  and  whose  west  side  falls  away  more  gently 
toward  Russian  River.  The  ridge  at  this  place  is  formed  entirely 
of  serpentine,  and  it  has  broken  off  in  successive  blocks  which  are 
faulted  downward  toward  the  river,  about.  1J  miles  away.  Behind 
the  fault  blocks  are  hollows  in  which  ponds  form.  The  wagon  road 
following  the  river  crosses  the  serpentine,  which  is  here  reduced  to 
mud  and  is  excessively  wet  much  of  the  time,  owing  probably  to 
water  that  follows  the  faults  and  oozes  out  at  this  place. 

The  principal  outcrop  of  magnesite  (see  PL  V,  A)  is  almost  at  the 
top  of  the  ridge.  It  is  apparently  15  to  20  feet  thick  and  30  feet 
long,  standing  between  4 and  5 feet  above  the  surface,  with  a westerly 
dip.  On  the  west  side  of  the  vein  slickensides  in  two  directions  are 
plainly  marked.  Two  smaller  outcrops  within  100  yards  S.  35°  E. 
(magnetic)  from  this  one  may  be  a continuation  of  the  same  vein. 

Several  other  veins  from  a few  inches  to  1 foot  thick  outcrop 
within  a few  feet  of  the  main  exposure,  and  200  feet  farther  west  are 
a number  of  smaller,  less  pure,  and  less  continuous  veins.  It  seems 
probable  that  the  veins  are  not  continuous  to  great  depth  owing  to 
the  recency  of  the  faulting,  by  which  they  would  have  been  cut  off. 

No  work  has  been  done  on  any  of  the  veins. 

The  magnesite  in  the  main  outcrop  is  white  and  remarkably  pure, 
especially  as  regards  its  freedom  from  lime.  A partial  analysis  by 
A.  J.  Peters,  at  the  St.  Louis  laboratory  of  the  United  States  Geo- 
logical Survey,  gave  the  following  result: 

Partial  analysis  of  magnesite  from  J.  M.  Hixon  ranch. 

[Solution  of  air-dried  material.] 


Silica  (Si02) ! 0.41 

Alumina  (A1203) 28 

Ferric  oxide  (Fe203) 12 

Lime  (CaO) 03 

Magnesia  (MgO) 47. 16 

Carbon  dioxide  (C02) 51.  88 


99.88 


22 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


As  occasionally  noted  at  other  places,  the  magnesite  shows  shrink- 
age cracks  (see  PL  VI,  A)  as  if  it  had  shrunk  after  deposition.  This 
suggests  the  probability  that  it  may  have  been  deposited  in  the  form 
of  a hydrous  carbonate. 

Smaller  deposits  are  said  to  occur  near  by,  but  they  were  not  seen 
by  the  writer. 

SONOMA  COUNTY. 

Creon  deposit. — Four  miles  north  of  Cloverdale  a number  of  mag- 
nesite veins  outcrop  in  extremely  irregular  serpentine  dikes,  on  a 
spur  running  southwestward  from  the  mountains  on  the  east  side  of 
the  Sonoma  Valley.  The  deposits  are  about  1,000  feet  (barometric 
measurement)  above  Cloverdale,  on  a steep  road,  but  the  haul  is  all 
down  hill. 

The  dikes  in  which  the  serpentine  occurs  are  in  places  but  a few 
feet  wide,  cutting  an  arkose  similar  to  that  in  San  Mateo  and  other 
Coast  Range  counties,  where  the  rock  is  Cretaceous  in  age.  They 
also  cut  some  finer  sediments.  Other  dikes  are  of  diabasic  charac- 
ter, and  there  is  considerable  glaucophane  schist  debris,  though  none 
was  seen  in  place.  The  relations  of  the  serpentine  to  the  country 
rock  are  obscure,  but  it  seems  probable  that  the  dikes  are  so  faulted 
as  to  be  locally  discontinuous. 

At  the  time  this  deposit  was  visited  (November  29,  1906)  work 
was  being  prosecuted  by  the  Magnesite  Products  Company,  of  West 
Berkeley,  Cal. 

Magnesite  veins,  from  6 inches  to  a foot  wide,  outcrop  on  the  sur- 
face at  a number  of  pieces,  but  they  show  little  continuity.  At  the 
main  outcrop,  which  was  close  beside  the  road,  a short  tunnel  cut  a 
pocket  of  magnesite  which  was  about  10  feet  wide,  15  to  16  feet  high, 
and  40  to  50  feet  long.  The  serpentine  is  so  faulted  that  if  the  mass 
ever  continued  onward  it  is  now  impossible  to  predict  where  the 
remainder  may  be  found.  About  500  tons  was  taken  out  and  the 
workings  abandoned. 

One-fourth  mile  N.  10°  E.  a vein  8 to  12  inches  thick  is  exposed 
alongside  the  road,  and  half  a mile  east  of  the  main  workings  a face 
of  magnesite  9 feet  high  is  exposed  below  the  road.  A tunnel  15 
feet  long  had  been  driven  into  it,  at  the  end  of  which  the  magnesite 
thinned  and  contained  serpentine. 

Besides  these  veins  there  were  a number  of  smaller  outcrops  at 
other  points  in  the  neighborhood. 

The  magnesite  in  the  worked  deposit  is  but  little  discolored  and 
portions  are  pure  white,  but  all  through  it  is  scattered  some  ser- 
pentine only  partially  altered  to  magnesite.  The  mass  has  been 
much  crushed  and  the  pieces  have  been  recemented  by  crystalline 
magnesite  of  a slightly  greenish  yellow  color,  which  forms  a layer 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  VI 


CRACKS  IN  MAGNESITE  APPARENTLY  DUE  TO  SHRINKAGE. 

A,  Compact  magnesite  from  Hixon  ranch,  Mendocino  County;  B,  Less  compact  magnesite  coated  with 
a thin  layer  of  quartz,  also  cracked,  from  locality  4 miles  northeast  of  Porterville. 


SONOMA  COUNTY. 


28 


about  one  thirty-second  of  an  inch  thick  around  the  fragments.  In 
places  colorless  fragile  platy  crystals  coat  the  cavities.  A partial 
analysis  by  A.  J.  Peters  of  a sample  as  nearly  representative  as  could 
be  selected  gave  the  following  results: 


Partial  analysis  of  magnesite  from  Creon  deposit. 
[Solution  of  air-dried  material.] 

Silica  (Si02) - - - 

Alumina  (A1203) 

Ferric  oxide  (Fe203) 

Lime  (CaO) 

Magnesia  (MgO) 

Carbon  dioxide  (C02) 


1.60 

.25 

1.09 

1.04 

45.20 

50.43 


99.61 

No  analysis  was  made  of  the  magnesite  from  the  other  veins,  which 
is  less  pure,  part  being  yellow  in  color. 

Eckert  ranch  deposits. — Three  deposits  of  magnesite  are  said  to 
occur  on  the  Eckert  ranch,  on  the  edge  of  the  valley  2 miles  east  of 
Cloverdale,  but  only  two  were  seen  by  the  writer.  The  more  north- 
erly is  not  more  than  200  yards  from  the  public  road.  Here  on  a 
soil-covered  hillside  a considerable  amount  of  magnesite,  roughly 
estimated  at  between  100  and  200  tons,  has  been  excavated  and 
piled  up.  The  hole  from  which  it  was  taken  has  been  so  filled  with 
dirt  that  nothing  could  be  seen  of  the  rocks  nor  of  magnesite  left  in 
place.  The  mineral  is  considerably  stained,  brownish  and  yellow, 
and  gives  the  impression  of  being  much  more  impure  than  it  really 
is.  Here  too  the  magnesite  is  considerably  cracked  and  the  apertures 
are  coated  with  a transparent  crystalline  magnesite,  which  at  first 
glance  looks  like  quartz. 

A partial  analysis  by  A.  J.  Peters  is  as  follows: 

Partial  analysis  of  magnesite  from  north  outcrop  on  the  Eckert  ranch. 

[Solution  of  air-dried  material.] 


Silica  (Si02) 0.51 

Alumina  (A1203) 1.98 

Ferric  oxide  (Fe203) 16 

Lime  (CaO) 59 

Magnesia  (MgO) 45.84 

Carbon  dioxide  (C02) 50.  80 


99.88 

In  a plowed  field,  a quarter  of  a mile  southeast  of  the  occurrence 
just  described,  several  rounded  outcrops  of  magnesite,  up  to  4 or  5 
feet  across,  occur  in  a line  through  a distance  of  about  75  feet.  There 
has  not  been  enough  excavation  to  show  whether  they  belong  to  one 
vein  or  whether  they  are  merely  nodules  of  large  size.  No  relation- 
ship between  these  outcrops  and  the  northern  deposit  can  be  traced. 


24 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


The  magnesite  is  much  whiter  and  purer  than  that  in  the  northern 
deposit,  and  is  nearly  free  from  lime.  A partial  analysis  by  A.  J. 
Peters  is  as  follows : 

Partial  analysis  of  magnesite  from  southern  outcrop  on  Eckert  ranch. 


Silica  (Si02) -• 0. 23 

Alumina  (A1203) 04 

Ferric  oxide  (Fe203) 20 

Lime  (CaO) 19 

Magnesia  (MgO) 46.88 

Carbon  dioxide  (C02) 51.57 


99.11  - 

George  Hall  ranch  deposit. — About  3 miles  southeast  of  Clover- 
dale,  on  the  George  Hall  ranch,  in  the  south  ba^ik  of  a deep  ravine 
running  toward  Russian  River,  there  is  a small  outcrop  of  magnesite 
about  20  feet  above  the  bed  of  the  stream.  Although  the  magnesite 
is  white  and  appears  to  be  of  good  quality  the  outcrop  is  only  4 or  5 
feet  broad  in  greatest  dimension,  so  that  it  gives  little  promise  of 
value. 

Pat  Cummings  claim. — The  Pat  Cummings  deposits  are  in  a ser- 
pentine hill  or  3 miles  S.  35°  W.  (magnetic)  from  Cloverdale, 
at  a height  of  about  1,200  feet  (barometric)  above  that  town.  At 
the  northernmost  occurrence  a few  tons  of  magnesite  has  been  mined 
and  thrown  out,  but  none  can  be  seen  in  place.  The  magnesite  is 
white,  but  like  that  in  most  of  the  other  deposits  has  been  much 
brecciated.  The  cracks  between  the  fragments,  however,  instead  of 
being  coated  with  crystalline  magnesite  as  is  usually  the  case,  are 
lined  with  clear  colorless  chalcedony,  so  that  the  percentage  of  silica 
present  is  large. 

About  one-fourth  of  a mile  farther  south  are  two  outcrops  of  impure 
magnesite  8 to  12  feet  in  diameter. 

Gilliam  Creek  deposits. — In  the  northwest  corner  of  sec.  6,  T.  8 N., 
R.  10  W.,  Mount  Diablo  base  and  meridian,  on  the  steep  western  side 
of  Gilliam  Creek,  400  or  500  feet  above  the  stream  and  about  7 miles 
northwest  of  Guerneville,  are  a number  of  large  outcropping  veins  of 
magnesite.  They  occur  in  a space  about  300  feet  long,  following  the 
creek,  and  about  100  feet  wide,  measured  along  the  slope.  The 
country  rock  is  as  usual  a serpentinized  basic  rock.  The  veins  stand 
out  boldly;  one  near  the  southern  side  of  the  claim  is  6 to  8 feet  thick 
and  rises  more  than  20  feet  above  the  hillside.  Great  masses  of  mag- 
nesite have  fallen  from  the  outcrop  and  lie  on  the  surface  or  are 
partly  buried  in  the  debris.  There  are  many  smaller  veins  and 
probably  one  or  two  as  thick  as  that  from  which  the  outcropping 
portions  have  broken,  so  that,  as  float  or  outcrop,  several  thousand 
tons  of  magnesite  in  large  pieces  are  in  sight.  Other  veins  undoubt- 


SONOMA  COUNTY. 


25 


edly  occur  north  of  this  deposit,  as  there  are  many  bowlders  of  magne- 
site in  the  creek.  Smaller  deposits  are  said  to  occur  down  the  creek 
(south)  from  the  main  outcrops.  Except  the  deposits  at  Red  Moun- 
tain, these  are  from  surface  indications  the  most  extensive  seen  by 
the  writer  in  California.  The  magnesite  here,  however,  contains  a 
greater  amount  of  impurities  than  that  at  Red  Mountain.  (Compare 
analyses  on  p.  36.) 

A partial  analysis,  made  by  A.  J.  Peters,  of  a sample  picked  to  be 
as  nearly  representative  as  possible,  was  as  follows: 

Analysis  of  magnesite  from  west  side  of  Gilliam  Creek. 


Silica  (Si02) 3.51 

Alumina  (A1203) 1.10 

Ferric  oxide  (Fe203) 80 

Lime  (CaO) 1.46 

Magnesia  (MgO) 43.65 

Carbon  dioxide  (C02) 49.16 


99.68 

This  magnesite  is  probably  too  impure  for  use  as  a material  for 
cement,  but  should  make  brick  which  would  compare  well  with  the 
Austrian,  and  is  good  for  gas  and  wood-pulp  bleaching. 

The  property  is  owned  by  the  Western  Carbonic  Acid  Gas  Company. 
About  a mile  of  new  road  was  necessary  to  connect  the  deposit  with  an 
established  highway,  and  this  was  being  constructed  at  the  time  of 
the  writer’s  visit  (December  3,  1906).  No  magnesite  had  then  been 
shipped  from  the  deposit. 

Madeira  deposit .a — The  Madeira  deposit  was  unknown  to  the  writer 
at  the  time  of  his  trip  into  Sonoma  County,  and  so  was  not  visited. 
It  is  in  sec.  31,  T.  9 N.,  R.  10  W.,  which  adjoins  on  the  north  the  sec- 
tion in  which  is  located  the  Western  Carbonic  Acid  Gas  Company’s 
claim,  and  is  said  to  be  a rather  extensive  deposit  of  magnesite  con- 
taining considerable  silica.  The  best  exposures  are  said  to  be  along 
a small  tributary  of  Gilliam  Creek.  It  will  be  necessary  to  build 
between  1 and  2 miles  of  wagon  road  before  the  magnesite  can  be 
hauled  to  the  railroad. 

Unnamed  deposits . — About  three-fourths  of  a mile  northwest  of  the 
Western  Carbonic  Acid  Gas  Company’s  deposit,  probably  in  sec.  36, 
T.  9 N.,  R.  11  W.,  near  the  top  of  a high  hill,  are  a number  of  magne- 
site veins  from  2 to  10  inches  or  more  in  thickness.  One  vein  about 
10  inches  thick  is  exposed  broadside  along  the  face  of  a bluff  perhaps 
30  feet  high.  The  quality  of  the  magnesite  here  is  apparently  very 
good,  though  a number  of  the  veins  contain  much  serpentine.  At 
one  place  there  is  a reticulated  vein  whose  individual  members  are 
from  4 to  8 inches  thick.  This  vein,  which  was  formerly  made  up  of 


a Data  furnished  by  Chester  Naramore. 


26 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


opaque  white  magnesite  containing  some  serpentine,  has  been  much 
broken.  Around  the  fragments  light-green,  radially  crystallized  mag- 
nesite has  formed,  and  cavities  that  still  remained  have  been  filled 
with  milky  chalcedony.  The  mass  now  consists  largely  of  the  green 
crystalline  magnesite  and  is  striking  in  appearance.  It  is  said  that 
at  one  time  an  attempt  was  made  to  work  the  deposit  for  ornamental 
stone,  under  the  impression  that  it  was  Mexican  onyx  (onyx  marble). 
There  are  too  many  imperfections  in  the  material  to  make  it  desirable 
for  this  use.  An  old  road,  now  fallen  into  bad  repair,  leads  past  the 
deposit  to  another  road  running  to  Healdsburg,  which  is  about  11 
miles  distant.  Should  it  become  desirable  to  work  these  veins,  the 
railroad  could  probably  be  reached  more  easily  at  Healdsburg  than 
at  Guerneville.  Magnesite  float  was  seen  in  a number  of  creeks  in 
the  neighborhood,  showing  the  existence  of  other  deposits,  whose 
extent  is  unknown. 

Red  Slide  deposits. — The  Red  Slide  deposits  are  situated  near  a 
natural  feature  known  by  that  name  in  the  valley  of  East  Austin 
Creek,  in  T.  9 N.,  R.  11  W.,  about  84  miles  by  road  north  of  Cazadero. 
The  serpentine  on  the  high  hill  in  which  the  deposits  are  situated  is 
stained  with  iron  oxide,  and  there  is  so  much  slipping  of  the  rock 
that  vegetation  can  not  exist  on  that  portion  of  the  hill,  whence  the 
name  “Red  Slide.”  It  may  be  seen  from  other  hilltops  for  long  dis- 
tances and  so  is  a familiar  landmark. 

A large  belt  of  serpentine,  whose  limits  are  unknown,  runs  through 
this  portion  of  the  country,  and  in  it  occur  the  magnesite  deposits. 
In  the  group  examined,  which  lies  on  the  west  side  oNf  the  creek,  there 
are  several  outcrops  up  to  5 and  6 feet  wide  and  a number  of  smaller  ' 
ones. 

At  the  time  the  deposits  were  visited  (December  4,  1906)  the 
Sonoma  Magnesite  Company  was  doing  development  work  on  them. 
Two  tunnels  had  been  run  into  the  hill,  one  a few  feet  above  the  creek 
and  the  other  about  80  feet  higher  up  the  hill  and  100  feet  or  so 
upstream. 

The  upper  tunnel  was  well  driven,  93  feet  long,  6 feet  high,  and  7 
feet  wide.  Three  veins  5 to  6 feet  thick  and  a number  of  smaller 
ones  had  been  cut.  There  was  but  little  work  to  show  the  extent  of 
the  veins  beyond  their  thickness  and  they  could  not  be  followed  on 
the  surface.  Much  more  development  work  is  said  to  have  been 
done  since  then.  At  one  point  magnesite  was  said  by  Mr.  E.  W. 
Arnold,  the  superintendent,  to  have  formed  during  the  preceding 
winter,  and  it  gave  much  evidence  of  being  a recent  deposit.  Water 
trickled  over  a face  of  magnesite  exposed  by  mining,  and  a soft  nodular 
deposit,  somewhat  resembling  a spring  deposit  of  calcite,  covered 
that  portion  of  the  wall.  Owing  to  the  fact  that  shrinkage  cracks 
are  frequently  found  in  magnesite,  the  question  arose  in  the  writer’s 
mind  as  to  whether  magnesite  was  not  deposited  as  a hydrous  car- 


SONOMA  COUNTY. 


27 


bonate,  and  a specimen  of  the  material  was  collected  and  later  tested 
in  the  Geological  Survey  chemical  laboratory,  where  it  was  pro- 
nounced anhydrous.  Evidence  of  considerable  faulting  appears  in 
the  upper  tunnel  and  small  veins  show  dislocations  of  a foot  or  less. 
One  of  the  larger  veins  was  followed  for  but  a few  feet  before  it  gave 
out. 

The  lower  level  was  200  feet  long  and  of  the  same  cross  section  as 
the  upper  one.  It  started  in  on  a vein  of  magnesite  which  appeared 
to  be  about  9 feet  wide  (PI.  V,  B),  but  the  entrance  is  not  at 
right  angles  to  the  vein,  and  the  magnesite  on  the  right  side  of  the 
vein  grades  into  serpentine.  There  is  probably  not  more  than  6 feet 
of  clear  magnesite.  The  tunnel  did  not  follow  this  vein  far  and  only 
one  other  was  cut.  This  second  vein  has  been  faulted,  and  though 
apparently  about  6 feet  wide,  but  little  could  be  told  of  its  extent. 
The  attempt  to  crosscut  the  veins  cut  in  the  upper  tunnel  was  unsuc- 
cessful. It  seems  altogether  likely  that  the  general  remarks  about 
the  indefinite  extension  of  magnesite  veins  in  any  direction  will  apply 
with  full  force  here.  These  veins  will  probably  be  found  to  be  of 
much  less  length  and  depth  than  might  be  expected  from  their  width, 
if  they  were  to  be  judged  by  the  ordinary  characteristics  of  quartz 
veins. 

The  magnesite  is  of  a creamy  color  and  contains  considerable  silica. 
It  is,  however,  remarkably  free  from  lime.  A partial  analysis,  by 
A.  J.  Peters,  of  a sample  selected  to  represent  as  nearly  as  possible 
the  average  rock  gave  the  result  stated  below.  There  is  no  doubt 
that  better  or  worse  specimens  might  be  taken. 

Analysis  of  magnesite  from  Red  Slide  deposits. 


Silica  (Si02) 7.67 

Alumina  ( A1203) 26 

Ferric  oxide  (Fe203) 29 

Lime  (CaO) 04 

Magnesia  (MgO) 43.42 

Carbon  dioxide  (C02) 48.08 


99.76 

A large  quantity  of  magnesite,  estimated  by  Mr.  Arnold  to  be 
almost  2,000  tons,  though  this  figure  seemed  somewhat  large  to  the 
writer,  lies  on  the  dumps.  There  is  also  a good  deal  of  float  magne- 
site in  the  creek.  The  road  from  the  workings  to  Cazadero  crosses  a 
mountain  with  grades  so  steep  that  it  is  impossible  to  haul  the  mag- 
nesite out  at  a profit.  The  road  to  Guerneville  is  as  bad,  or  worse, 
and  longer,  so  that  at  present  the  magnesite  can  not  be  marketed. 
Should  a way  to  haul  the  rock  out  be  obtained,  the  company  expects 
to  make  artificial  stone  and  tiles.  The  company  claims  to  have  a 
much  better  deposit  2\  miles  farther  up  the  creek,  where  a vein  is 
said  to  be  from  10  to  25  feet  thick  and  to  have  been  followed  for  900 
feet. 


28 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


Norton  ranch  deposits .a — On  the  Ed.  Norton  ranch,  along  Dry  Creek, 
10  miles  northwest  of  Healdsburg,  is  a deposit  of  rather  siliceous 
magnesite  in  large  rounded  chunks  lying  upon  serpentine  and  over- 
lain  by  clay  and  black  soil.  There  is  no  outcrop,  and  the  magnesite 
is  exposed  only  by  trenches. 

NAPA  COUNTY. 

General  remarks. — Like  all  the  other  counties  along  the  Coast 
Range,  Napa  County  has  a rough  topography,  so  that  railroad  and 
wagon-road  building  over  most  of  it  is  difficult.  The  beautiful  Napa 
Valley,  from  1 to  4 miles  wide,  runs  the  whole  length  of  the  western 
side  of  the  county,  and  east  of  it,  separated  by  rough  hills,  lie  Chiles 
and  Pope  valleys,  of  much  less  extent.  Only  in  the  Napa  Valley  is 
there  a railroad,  though  projects  for  an  electric  road  to  traverse  both 
of  the  other  valleys  on  its  way  to  Lake  County  have  been  agitated 
for  many  years.  At  one  time  grading  was  done  over  a part  of  the 
route,  and  later  another  company  constructed  a road  for  a portion  of 
the  distance  through  the  Napa  Valley. 

All  the  known  deposits  in  this  county  are  situated  east  of  the  Napa 
Valley,  with  rather  long  and,  in  some  cases,  difficult  hauls  to  the 
railroad.  Rutherford  is  the  most  easily  reached  station  and  the 
road  through  Conn  Canyon  is  the  first  stretch  of  the  route  to  any  of 
the  deposits. 

Walters  or  White  Rock  deposit. — The  deposit  bearing  this  name  is 
located  in  the  NE.  \ sec.  11,  T.  9 N.,  R.  5 W.,  on  the  east  side  of  Pope 
Valley,  22  miles  northeast  of  Rutherford.  The  distance  from  the 
railroad  makes  hauling  expensive,  and  the  claim,  which  was  never 
worked  on  a large  scale,  has  made  no  production  for  several  years. 
The  proposed  electric  road  from  San  Francisco  to  Lake  County,  if 
built,  will  pass  within  4 miles  or  less  of  the  deposit,  and  the  claim 
will  then  be  in  an  excellent  position  to  ship  magnesite. 

The  deposit  is  situated  about  three-fourths  of  a mile  from  a public 
road  in  a hill  of  serpentinized  lherzolite,  about  400  feet  (barometric 
measurement)  above  the  valley.  It  is  composed  of  a large  number 
of  veins  whose  exposures  range  in  width  from  a fraction  of  an  inch 
to  12  feet  and  lies  on  both  sides  of  a small  ravine  that  forms  an 
amphitheater,  with  an  easy,  straight  southward  grade  to  the  valley, 
making  an  almost  ideal  place  to  work  with  an  aerial  tram. 

The  veins  are  in  three  principal  groups,  two  of  which  lie  on  the 
east  side  of  the  ravine  and  the  other  on  the  west.  The  main  group 
on  the  east  side  comprises  three  large  veins  of  magnesite  that  can  be 
definitely  traced  for  distances  of  about  140,  250,  and  230  feet,  with 
strikes  of  N.  28°,  30°,  and  45°  W.,  respectively.  At  their  north  ends 
the  western  and  eastern  veins  are  but  30  feet  apart,  and  the  middle 

a Description  furnished  by  Chester  Naramore. 


NAPA  COUNTY. 


29 


vein  probably  converges  with  the  eastern  one.  A shallow  shaft  on 
the  western  vein  shows  its  dip  to  be  50°  N.  62°  E.  The  veins  stand 
out  boldly  and  can  be  seen  from  any  part  of  the  valley  not  hidden 
by  hills.  (See  PL  V,  C.)  Longitudinal  faults  occur  in  both  of 
the  outer  veins.  Between  the  large  veins  are  many  smaller  ones 
having  a general  parallelism  to  the  main  bodies.  At  its  widest  ex- 
posure the  western  vein  is  about  10  feet  thick,  of  which  about  5 feet 
on  the  foot  wall  is  solid  white  magnesite,  although  the  upper  5 feet 
on  the'  hanging-wall  side  contains  many  inclusions  of  serpentine. 
The  structure  of  the  eastern  vein  is  similar,  and  in  places  the  magne- 
site may  be  seen  grading  into  the  country  rock;  it  is  about  12  feet 
wide  where  exposed  in  a shallow  crosscut.  In  the  middle  vein  a 
width  of  18  inches  to  5 feet  of  clear  white  magnesite  is  exposed. 
There  has  been  some  crushing  of  the  magnesite  and  the  broken  par- 
ticles have  been  cemented  with  yellowish,  less  pure  material.  Part 
of  the  magnesite  has  formed  in  yellowish  botryoidal  masses  that  are 
rather  impure.  Some  crystalline  magnesite,  similar  to  that  of  Chiles 
Valley,  is  found  in  the  crevices.  It  is  said  that  1,250  tons  was  mined 
between  1894  and  1899,  being  simply  broken  from  the  exposed  faces 
of  the  veins. 

A second  group  with  a more  northerfy  strike  lies  100  feet  or  more 
above  the  veins  just  described.  The  veins  forming  this  group  are 
smaller,  running  from  2 inches  to  2 feet  in  width,  and  the  larger  of 
these  are  impure.  There  are  also  many  scattered  veins  in  the  inter- 
vening space. 

On  the  west  side  of  the  ravine,  200  to  250  feet  from  the  veins  first 
described,  is  a third  group  with  a strike  between  north  and  north- 
west. The  largest  vein  is  4 to  6 feet  wide;  and  seven  others  from  1 
to  2 feet  wide  occur  within  125  feet.  All  appear  to  be  of  excellent 
quality.  It  would  seem  possible  to  blast  out  the  whole  of  the  rock 
through  this  distance  and  hand-pick  it  at  a profit  should  the  deposits 
again  be  worked. ' A prospect  tunnel  was  run  into  the  hill  near  these 
veins  and  struck  an  irregular  vein  of  crushed  magnesite  at  the  end. 

Snowflake  and  Blanco  claims. — Magnesite  was  mined  by  Bartlett  & 
Stanley  at  a place  about  2 miles  south  of  the  old  Chiles  mill,  in  Chiles 
Valley,  and  10  miles  from  Rutherford,  for  a number  of  years,  but 
the  mine  has  not  been  operated  since  1900,  as  it  is  too  far  from  the 
railroad  to  compete  with  points  having  better  shipping  facilities. 

Here  also  the  country  rock  is  the  serpentine  of  the  Coast  Range, 
inclined  to  a dark-green  or  blue-black  color.  The  deposits  are  on 
the  west  side  of  the  valley,  in  a small  serpentine  hill  skirted  by  a pub- 
lic road,  and  consist  of  a number  of  veins  which  range  in  thickness 
from  1 foot  to  6 feet  and  are  said  to  have  been  as  much  as  12  feet  wide. 
Where  seen,  however,  the  larger  veins  were  considerably  mixed  with 
serpentine  and  other  impurities.  Marked  faulting  occurs  with  the 


30 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


veins,  and  both  the  hanging  and  foot  walls  are  generally  fault  planes. 
The  serpentine  is  much  broken  and  greatly  decomposed  in  the  neigh- 
borhood of  the  veins,  the  interstices  being  filled  by  smaller  veins  of 
magnesite. 

On  the  foot  walls  of  several  of  the  veins  extensive  silicification  has 
taken  place,  the  serpentine  being  hardened  through  2 or  3 feet.  The 
veins  are  locally  brecciated  and  cemented  with  less  pure  material  of 
yellowish  color,  the  original  magnesite  being  a clear  white.  At 
many  places  in  the  brecciated  portions  each  fragment  is  covered  by 
magnesite  in  radial  crystals,  forming  a coating  up  to  half  an  inch 
thick  and  varying  in  color  from  crystalline  clearness  to  delicate 
green  and  yellowish  green.  Cracks  in  the  serpentine  are  also  filled 
with  the  same  crystalline  magnesite.  This  material  is  strikingly 
different  from  the  ordinary  magnesite,  which  shows  no  crystal 
form  to  the  unaided  eye.  In  places  crevices  in  the  veins  have  a 
velvety  black  coating  of  pyrolusite  (manganese  dioxide),  making 
the  rock  look  as  if  it  were  coated  with  lampblack.  A small  amount 
of  chromite  has  been  found  in  the  neighborhood,  but  not  in  paying 
quantities.  Partial  analyses  of  magnesite  from  this  mine  are  given 
below : 


Partial  analyses  of  magnesite  from  the  Bartlett  6c  Stanley  mine , Chiles  Valley. 


1. 

2. 

3. 

Silica  (Si02)  - - - 

2. 15 
1.22 

1. 16 
5.28 

41.01 

48.72 

1.81 

} .08 

Trace. 

46.55 

51.25 

.32 

6.68 
15. 10 

Alumina  (AI2O3) 

Ferric  oxide  (Fe203) 

Lime  (CaO) 

Magnesia  (MgO) 

37.23 

40.98 

Carbon  dioxide  (CO2) 

Water  and  undetermined 

99. 54 

100.00 

99.  99 

Analysts:  No.  1,  P.  H.  Bates,  United  States  Geological  Survey;  Nos.  2 and  3,  Abbott  A.  Hanks, 
San  Francisco,  October  1, 1903. 


Specimen  No.  1 was  collected  by  the  writer  and  was  as  near]y 
representative  as  was  possible  to  select;  No.  2 was  probably  a picked 
sample,  and  No.  3 was  of  a poor  quality,  not  shipped.  The  lime 
content  of  the  first  specimen  is  very  high. 

During  the  time  that  the  mine  was  worked  probably  10,000  to 
12,000  tons  of  magnesite  was  taken  out  and  calcined.  As  pure 
magnesite  loses  more  than  half  its  weight  by  being  calcined,  a large 
saving  was  made  in  haulage  by  getting  rid  of  the  carbon  dioxide 
when  the  material  was  to  be  used  as  magnesia.  A four-sided  shaft 
furnace,  built  of  serpentine  and  sandstone  blocks  and  lined  with  fire- 
brick, was  used.  It  was  about  15  feet  high  and  from  3 to  5 feet 
across.  The  furnace  was  fired  from  the  four  sides  at  the  base  of  the 
shaft,  largely  with  manzanita,  a hard-wooded  shrub  making  a hot 


SANTA  CLARA  COUNTY. 


31 


fire,  and  the  calcined  magnesite  was  withdrawn  from  below.  The 
waste  magnesite  fines  below  the  furnace  have  compacted  noticeably 
from  recarbonation. 

Priest  deposit.0' — D.  C.  Priest  has  a magnesite  deposit  in  Chiles 
Valley,  in  sec.  23,  T.  8 N.,  R.  4 W.,  about  13  miles  from  Rutherford. 
One  2-foot  and  one  18-inch  vein  are  exposed,  well  up  a hillside,  and 
magnesite  of  a rather  poor  quality  is  exposed  in  a lower  opening.  No 
work  has  been  done  on  the  deposit  for  a number  of  years. 

Russell  deposit.0-— E.  T.  Russell  holds  a claim  in  sec.  24,  T.  8 N., 
R.  4 W.,  on  which  several  small  magnesite  veins  outcrop.  About 
25  tons  was  shipped  at  one  time.  The  deposit  is  4 miles  from  a 
road  and  15  miles  from  Rutherford. 

Matthai  deposits.0 — Frank  Matthai  formerly  held  a claim  known 
as  the  “North  mine”  in  Soda  Creek  canyon,  in  the  NE.  \ sec.  35, 
T.  8 N.,  R.  4 W.,  near  the  public  road.  Irregular  veins  and  masses 
of  magnesite  several  feet  thick  outcrop  in  serpentine  on  this  claim. 
Bartlett  & Stanley  mined  the  larger  masses  by  open  cuts  in  1895,  but 
the  property  has  been  idle  since.  Much  magnesite  still  remains  in 
sight. 

The  “South  mine,”  also  held  by  Mr.  Matthai,  lies  a quarter  of  a 
mile  southeast  of  the  “North  mine,”  on  the  other  side  of  a low 
ridge,  on  the  north  bank  of  Greasy  Camp  Creek.  A 5-foot  vein  of 
clear  white  magnesite  outcrops  along  the  creek  for  about  30  feet, 
dipping  into  the  hill  at  a low  angle.  At  the  time  the  mine  was 
visited  (1905)  two  open  cuts  and  a short  tunnel  had  been  made,  and 
about  100  tons  of  magnesite  was  piled  up. 

SANTA  CLARA  COUNTY. 

Deposit  near  Coyote. — A small  deposit  of  magnesite  occurs  on  W.  W. 
Burnett’s  ranch,  about  3 miles  northeast  of  the  Coyote  railroad 
station  and  half  a mile  north  of  the  summit  of  the  Metcalf  road. 
The  deposit  occurs  near  the  top  of  the  east  slope  of  a hill  several 
hundred  feet  high  in  a belt  of  impure  serpentine,  which  weathers  in 
rough,  irregular  forms.  The  exposed  portion  of  the  vein  is  about 
100  feet  in  length  and  4 to  10  feet  wide,  striking  N.  35°  W.  (mag- 
netic), apparently  with  a nearly  vertical  dip.  A ravine  cuts  off 
the  vein  on  the  south,  but  some  pebbles  of  magnesite  were  found 
on  the  south  side,  so  that  there  may  be  on  that  side  either  another 
deposit  or  an  extension  of  this  one.  The  main  part  of  the  vein  is  of 
good  quality,  but  a part  of  the  magnesite  is  rather  siliceous  and  con- 
tains fragments  of  serpentine  now  almost  entirely  replaced  by  silica 
and  magnesite.  The  fragments  on  the  surface  south  of  the  ravine 
are  still  more  impure. 


a Data  furnished  by  Chester  Naramore. 


32 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


A partial  analysis  by  A.  J.  Peters  of  a specimen  from  the  large  vein 
gave  the  following  result: 

Partial  analysis  of  magnesite  from  W.  W.  BurnetVs  ranch , Coyote. 


Silica  (Si02) 0. 30 

Alumina  (A1203) . . .16 

Ferric  oxide  (Fe203) 38 

Lime  (CaO) 1.  34 

Magnesia  (MgO) 45.86 

'Carbon  dioxide  (C02) 51.  80 


99.74 

The  magnesite  seems  to  be  suitable  for  brick,  g%s  making,  and 
paper  making,  but  probably  has  too  much  lime  to  make  good  oxy- 
chloride cement. 

As  is  usually  the  case,  the  serpentine  is  much  more  decayed  near 
the  vein  than  in  other  places.  On  the  west  wall  of  the  vein  the  ser- 
pentine is  so  much  impregnated  with  magnesite  that  it  has  a gray 
appearance  for  a thickness  of  several  feet.  In  other  places  it  has  a 
glassy  aspect  over  small  areas,  but  the  quantity  is  too  small  and  the 
serpentine  is  too  much  cracked  to  permit  its  utilization  as  an  orna- 
mental stone.  Many  small  veins  of  cryptocrystalline  quartz  cut  the 
serpentine  in  various  directions.  In  some  of  the  veins  are  small  vugs 
showing  crystallized  quartz. 

Bay  Cities  Water  Company’s  land. — A couple  of  miles  northeast  of 
Morgan  Hill  station  Coyote  Creek  turns  abruptly  to  the  west  from  a 
northward  course  and  flows  through  a serpentine  ridge  into  the  Santa 
Clara  Valley  by  way  of  a narrow  cut,  on  the  north  side  of  which  are 
several  veins  of  magnesite.  The  serpentine  in  which  they  occur  is 
similar  to  that  east  of  Coyote  station,  and  may  be  a part  of  the  same 
dike.  The  lowest  vein  is  perhaps  250  yards  west  of  San  Felipe  Creek, 
which  joins  Coyote  Creek  at  its  westward  bend.  The  outcrop  of  the 
vein  strikes  N.  85°  E.,  is  about  10  feet  wide  and  50  feet  long,  and 
forms  the  point  of  a small  hill. 

The  magnesite  is  made  up  of  rounded  irregular  particles  ranging 
from  half  an  inch  downward  in  diameter  (see  PL  VII,  B)y  cemented 
by  siliceous  magnesite,  which  for  an  inch  or  more  from  the  surface 
is  stained  red  by  iron.  Many  chunks  of  iron-stained  quartz  2 feet 
or  more  in  diameter  lie  on  the  ground  near  the  outcrop.  No  work 
has  been  done  on  this  vein. 

About  100  feet  farther  up  the  hill  is  a larger  deposit  of  rather 
impure  magnesite,  which  does  not  carry  so  much  silica,  but  has  much 
serpentine  mixed  through  it.  A number  of  extremely  irregular  veins 
interlace  through  an  area  200  feet  long  by  50  to  100  feet  wide.  In 
places  the  magnesite  has  an  oolitic  structure,  analogous  to  the  struc- 
ture of  the  vein  lower  down  the  hill,  but  the  particles  are  all  small, 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  Vll 


STRUCTURE  OF  MAGNESITE  ON  BAY  CITIES  WATER  COMPANY'S  LAND  ON  COYOTE 

CREEK. 

^1,  Specimen  from  Ihe  upper  deposit,  showing  a natural  surface;  B,  Specimen  from  the  lower 
deposit,  showing  a smoothly  ground  surface.  Both  natural  size. 


SANTA  CLARA  COUNTY. 


33 


only  a few  grains  reaching  one-eighth  inch  in  longer  diameter.  (See 
PI.  VII,  A.)  At  the  outer  part  the  fragments  are  separated  by 
talcose  matter,  but  the  mass  becomes  gradually  more  compact  until 
the  particles  coalesce  and  form  dense,  solid  magnesite.  The  prin- 
cipal vein  runs  almost  parallel  with  the  course  of  the  hill,  and  a face 
10  to  20  feet  high  has  been  exposed  by  a cut.  In  places  segregations 
of  clear-white  magnesite  reach  2 to  3 feet  in  thickness,  but  other 
portions  of  the  vein  are  but  a few  inches  thick.  The  material  could 
be  hand  picked  and  a fair  to  good  quality  obtained. 

An  old  sheet-iron  furnace  is  in  ruins  on  the  ground,  and  it  is  said 
that  an  attempt  was  made  to  calcine  the  magnesite  some  years  ago. 
Several  carloads  of  the  raw  material  are  reported  to  have  been  shipped. 

Mrs.  A.  F.  Cochrane’s  land. — About  1J  miles  south  of  the  junction 
of  Coyote  and  San  Felipe  creeks  and  about  3J  miles  from  Morgan 
Hill  station,  on  the  land  of  Mrs.  A.  F.  Cochrane,  is  a rather  bold 
outcrop,  several  feet  wide,  of  a fine-grained  buff-colored  magnesite, 
which  can  be  followed  for  more  than  200  feet  up  the  hill. 

The  serpentine  shows  much  silicification  and  iron  staining.  In 
places  blocks  8 or  10  feet  thick  are  almost  tvholly  replaced  by  iron- 
stained  quartz.  Elsewhere  the  cracks  in  the  serpentine  have  been 
filled  with  quartz,  very  much  as  at  other  deposits  the  cracks  have 
been  filled  with  magnesite.  The  serpentine  between  the  quartz  veins 
is  much  decayed  and  in  places  drops  out,  leaving  an  irregular  skeleton 
of  silica  much  stained  with  yellow  and  red  iron  oxides.  The  great 
amount  of  iron  present  in  this  locality  is  very  noticeable,  and  to  it 
the  magnesite  probably  owes  its  buff  color,  although  the  analysis 
shows  but  0.18  per  cent  of  ferric  oxide.  Silica  makes  nearly  half  of 
the  rock.  A partial  analysis  by  A.  J.  Peters  is  as  follows: 

Partial  analysis  of  magnesite  from  Mrs.  A.  F.  Cochrane's  land,  near  Morgan  Hill. 

[Solution  of  air-dried  material.] 

Silica  (Si02) 

Alumina  (A1203) 

Ferric  oxide  (Fe203) 

Lime  (CaO) 

Magnesia  (MgO)... 

Carbon  dioxide  (C02) 

99.45 


49.85 

3.45 

.18 

.48 

21.53 

23.96 


In  places  small  fragments  of  dull-yellow  magnesite  are  included 
in  the  quartz.  It  is  reported  that  some  work  was  done  on  the  deposit 
in  1897  and  that  several  carloads  of  magnesite  were  shipped  to  San 
Francisco. 

Red  Mountain  deposits. — Near  Livermore,  a town  48  miles  south- 
east of  San  Francisco,  there  are  a number  of  magnesite  deposits,  of 
which  the  only  one  now  being  worked  is  that  of  the  American  Mag- 
51136— Bull.  355—08 3 


84 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


nesite  Company,  32  miles  southeast  of  Livermore  on  Red  Mountain, 
in  the  northeast  corner  of  Santa  Clara  County,  along  the  Stanislaus 
County  line.  A number  of  the  company’s  claims  are  located  in  the 
latter  county.  From  Livermore  an  excellent  road  follows  up  the 
Arroyo  Mocho,  crossing  into  and  running  down  the  Arroyo  Colorado. 
The  maximum  grade  for  the  haul  from  the  mine  is  said  to  be  3 per 
cent.  At  the  mines  the  company  has  erected  good  buildings  and 
roads,  and  an  aerial  tram  2,500  feet  long,  with  a capacity  of  100  tons 
per  ten-hour  day,  delivers  the  magnesite  to  bunkers,  from  which  it 
is  loaded  into  wagons  for  hauling  to  Livermore.  An  attempt  was 
made  to  haul  the  magnesite  with  oil-burning  traction  engines  draw- 
ing two  iron  wagons  carrying  17  J tons  each,  and  two  such  trains 
were  put  into  operation,  but  are  reported  to  have  been  unsuccessful. 
The  haul  to  the  railroad  is  very  long  for  a product  of  no  greater  value 
than  magnesite,  and  can  scarcely  be  profitable.  The  magnesite  is 
shipped  to  Oakland,  where  the  company’s  factories  for  brick,  carbon 
dioxide,  and  other  products  are  situated.  The  mine  offices  and 
other  buildings  are  located  near  springs  that  give  sufficient  water 
for  the  engines,  the  mine,  and  other  purposes.  The  country  rock  is 
lherzolite  and  peridotite,  in  some  places  much  serpentinized  and  in 
others  remarkably  fresh.  The  magnesite  occurs  in  the  more  altered 
portions. 

Although  these  deposits  have  been  known  for  a long  time,  they 
were  not  worked  until  1905,  owing  to  their  distance  from  a railroad. 
They  occur  in  a number  of  veins  in  a group  around  a small  valley,  so 
arranged  as  to  be  excellently  located  for  working  by  adits  and  an 
aerial  tram.  Just  how  many  veins  there  are  can  not  be  stated,  as 
the  brief  time  at  the  writer’s  disposal  did  not  allow  examination  of 
the  smaller  ones.  Owing  to  debris  and  faulting  it  is  not  possible  to 
tell  whether  many  of  the  outcrops  belong  to  the  same  veins  as  neigh- 
boring ones  or  whether  they  are  separate  deposits.  In  the  immediate 
vicinity  there  are,  however,  probably  10  or  12  veins,  and  possibly 
more,  2 feet  or  over  in  thickness,  all  of  which  could  be  well  worked 
with  but  slight  changes  in  the  plant  installed. 

The  veins  stand  out  prominently  in  the  bright  sunshine  of  the  val- 
ley and  are  almost  dazzlingly  white,  so  that  they  can  be  seen  from  the 
higher  hills  miles  away.  One  of  the  veins,  called  the  “Mammoth,” 
stands  fully  10  feet  above  the  hillside. 

The  magnesite  shows  a number  of  peculiarities  in  weathering. 
Some  of  the  surfaces  weather  into  a pattern  that  looks  like  sun 
cracks  in  mud  (see  PI.  IV,  B),  wdth  flatly  oval  surfaces  from  one- 
eighth  to  three-fourths  of  an  inch  wide  between  the  cracks.  In 
places  there  are  fluted  surfaces,  such  as  occur  on  exposed  limestones, 
but  in  narrower  lines  (see  PI.  Ill,  A),  and  locally  the  weathered 
surface  is  thickly  studded  with  sharp  points.  Many  exposed  sur- 
faces are  covered  with  a white  powder  which  has  been  supposed  to 


SANTA  CLARA  COUNTY. 


35 


be  magnesium  oxide  or  hydromagnesite,  but  which  has  been  deter- 
mined to  be  another  form  of  magnesite.  Underground  also  nodules 
or  portions  of  veins  of  magnesite  in  places  have  turned  to  this  powder, 
leaving  a core  of  solid  material.  Mr.  C.  H.  Spinks,  the  superintend- 
ent of  the  mines,  told  the  writer  that  certain  other  veins  a few  miles 
distant,  belonging  to  the  company,  carried  very  much  more  of  this 
powder.  Powdery  magnesite  has  been  described  as  occurring  also  in 
South  Africa.  (See  p.  60.)  Why  it  should  take  this  form,  breaking 
down  from  the  solid  state  without  apparent  chemical  change,  is 
unknown. 

Only  one  vein  on  the  Alameda  claim,  near  the  top  of  the  ridge, 
was  being  worked  in  November,  1905,  when  the  claims  were  visited, 
and  the  first  magnesite  was  shipped  in  that  month.  This  vein  has 
a strike  of  N.  30°  W.  (magnetic),  with  a steep  southwesterly  dip.  It 
ranges  in  thickness  from  15  to  40  feet,  and  could  be  definitely  followed 
for  about  300  feet  S.  30°  E.  from  faults  against  which  it  ends  at  the 
north.  Whether  the  vein  has  been  faulted  off  or  whether  its  ter- 
mination was  originally  fixed  by  the  fault  was  not  clear.  Although 
the  fault  mud  and  breccia  contains  some  crushed  magnesite,  this  may 
come  from  other  sources.  Veins  of  rosiny  opal  and  an  aluminous 
siliceous  material,  1 inch  to  3 feet  thick,  occur  along  the  fault.  The 
magnesite  is  also  badly  cut  and  crushed  by  faults  and  contains  in 
places  much  serpentine  and  some  of  the  aluminous  siliceous  veins. 

On  approaching  the  vein  through  the  tunnel  one  sees  that  the  ser- 
pentine is  greatly  decayed  and  is  cut  in  every  direction  by  innumer- 
able small  veins  of  magnesite,  crossing  each  other  at  all  angles.  Here 
and  there,  in  veins  which  do  not  exceed  2 or  3 inches  in  thickness,  sud- 
den enlargements  occur,  which  may  be  3 feet  in  diameter  and  almost 
equidimensional.  These  are  referred  to  as  “bowlders,”  but  they  have 
nothing  in  common  with  bowlders  beyond  size  and  shape.  Some  of 
the  smaller  nodules  are  partly  composed,  mostly  in  the  outer  portion, 
of  aluminous  and  siliceous  material,  the  inner  portion  appearing  to 
be  comparatively  pure  magnesite.  This  material  seems  to  be  a 
replacement  of  the  magnesite  similar  to  the  replacement  of  calcite  by 
silica.  The  small  veins  grow  in  number  and  in  thickness  until  by 
steady  gradation  the  mass  of  comparatively  pure  magnesite  is  reached. 
At  other  points  the  vein’s  walls  are  abrupt  and  are  probably  delim- 
ited by  faults.  The  vein  was  pierced  by  several  adits  on  different 
levels,  and  a crosscut  at  one  place  entered  the  vein  for  35  feet  without 
going  through  it.  A drill  hole  8 feet  long  at  the  end  of  the  crosscut  was 
said  not  to  have  reached  the  other  side.  The  magnesite  is  pure 
white,  the  crosscut  looking  as  if  freshly  whitewashed.  As  is  to  be 
expected  in  a serpentine  area,  faults  have  cut  the  vein  in  a number 
of  places,  and  through  at  least  a portion  of  their  length  both  hanging 
and  foot  walls  are  fault  planes. 


36  MAGNESITE  DEPOSITS  OF  CALIFORNIA. 

At  several  places  pipes  or  nearly  vertical  channels,  6 inches  and 
upward  in  diameter,  now  largely  filled  with  clay,  have  been  cut 
through  the  magnesite  by  water.  The  walls  of  these*  channels  are 
much  smoother  than  those  of  most  similar  channels  cut  in  limestone, 
owing  probably  to  the  homogeneous  composition  of  the  magnesite. 
At  two  places  the  watercourses  were  large  enough  to  use  as  chutes. 

Mining  is  carried  on  by  means  of  an  open  cut,  in  which  the  magnesite 
is  quarried  and  allowed  to  fall  through  an  upraise  to  an  adit  below, 
whence,  it  is  moved  in  cars  to  the  aerial  tram.  The  tramway  drops 
600  feet  in  the  2,500  feet  to  the  bunkers.  The  skips  are  placed  500 
feet  apart  and  each  carries  1,000  pounds  of  magnesite. 

On  the  Canada  claim,  several  hundred  feet  down  the  hill  from  the 
worked  vein,  is  a large  irregular  outcrop  of  magnesite,  between  40 
and  50  feet  across,  which  had  not  been  prospected  at  the  time  the 
claim  was  visited.  Later  it  was  reported  that  a prospect  tunnel  run 
under  this  outcrop  had  shown  the  magnesite  to  contain  much  included 
serpentine. 

Just  across  the  ridge  from  the  point  at  which  mining  was  being 
carried  on  is  the  outcrop  of  the  u Mammoth’’  vein,  already  referred 
to,  which  stands  more  than  10  feet  above  the  hill  slope  on  its  lower 
side.  It  is  about  4 feet  thick  and  apparently  is  of  excellent  quality. 
It  had  not  been  prospected,  so  that  nothing  could  be  told  of  it 
beyond  its  outcrop. 

A number  of  other  veins  in  the  group  are  up  to  10  feet  wide  and 
at  least  one  can  be  followed  for  200  yards.  They  are  not  all  equally 
pure,  and  several  contain  a considerable  amount  of  included  ser- 
pentine. 

Extravagant  estimates  of  the  amount  of  magnesite  in  sight  have 
been  made,  but  though  the  amount  exposed  is  large,  the  develop- 
ment at  the  time  the  deposits  were  visited  was  not  extensive,  and 
from  the  outcrops  alone  but  two  dimensions  can  be  known,  so  that 
estimates  of  the  total  amount  available  are  but  little  better  than 
guesswork.  Ravines  cutting  across  the  strike  of  the  veins  do  not 
expose  them  and  show  that  they  are  continuous  for  long  distances. 

The  following  are  partial  analyses  of  magnesite  from  the  Alameda 
claim : 


Partial  analyses  of  magnesite  from  Alameda  claim , Santa  Clara  County. 


1. 

2. 

Rilioa.  (SiOj'i  

0.73 

.14 
.21 
.40 
46.  61 
51.52 

3.93 
} .20 
1. 16 

Alumina,  ( AI2O3')  

Ferric  oxide  (Fe20s)  

Tiimfi  CCa.O'l  

Magnesia  (MgO)  - . .. 

Carbon  dioxide  (C^j)  

09.  61 

5.29 

ALAMEDA  AND  STANISLAUS  COUNTIES. 


37 


Analysis  No.  1 was  made  by  A.  J.  Peters,  of  the  United  States 
Geological  Survey.  No.  2 was  made  by  E.  T.  Allen,  of  the  Carnegie 
Institution  geophysical  laboratory,  to  determine  the  amount  of  im- 
purities present,  preparatory  to  using  the  magnesite  in  his  experi- 
mental work.  Both  specimens  were  collected  by  the  writer,  and  the 
second  was  picked  out  for  its  whiteness  under  the  supposition  that 
it  would  be  especially  pure.  F.  E.  Wright  determined  microscopically 
that  the  silica  was  present  as  quartz,  and  not  as  combined  silica. 

Close  to  the  magnesite  veins,  about  250  yards  southeast  of  the 
present  workings,  are  small  impregnation  veins  of  chromite.  The 
chromite  occurs  in  grains  from  the  size  of  a pea  downward,  and  can 
be  clearly  seen  to  spread  from  joints  in  a serpentinized  peridotite. 
It  is  accompanied  by  a pale  lilac-colored  chlorite,  probably  either 
kotschubeite  or  kammererite.  A small  amount  of  work  has  been 
done  on  the  veins,  but  the  prospects  do  not  seem  to  have  been  encour- 
aging. A little  cinnabar  is  said  to  have  been  found  in  the  neighbor- 
hood, and  two  mercury  mines  are  being  developed  within  a radius 
of  4 or  5 miles. 

On  Cedar  Mountain,  in  Alameda  County,  the  company  had  also 
located  eight  magnesite  claims  which,  however,  were  not  being  worked 
and  were  not  visited. 

Other  Santa  Clara  County  deposits. — There  were  said  to  be  other 
deposits  in  the  neighborhood  of  Coyote,  but  the  locations  given  were 
so  indefinite  that  they  could  not  be  found.  Small  deposits  are  said 
to  occur  in  Alum  Bock  Park,  near  San  Jose,  and  in  the  vicinity  of  the 
mercury  mines  at  New  Almaden,  but  they  are  without  commercial 
importance.  From  the  amount  of  serpentine  in  the  county  it  is  rather 
to  be  expected  that  there  should  be  other  occurrences  of  magnesite. 

ALAMEDA  COUNTY.0 

King  claim.  —Two  miles  from  the  Arroyo  Mocho  road  and  22  miles 
southeast  of  Livermore,  on  the  King  claim,  several  small  veins  of 
magnesite  are  exposed  in  a cut.  There  has  been  no  production. 

Bantams  camp  deposit. — In  sec.  16,  . T.  5 S.,  R.  4 E.,  on  a narrow  ridge 
southwest  of  Banta’s  cabin  in  the  Arroyo  Mocho  canyon,  24  miles 
southeast  of  Livermore,  is  a small  outcrop  of  magnesite.  There  has 
been  no  development. 

STANISLAUS  COUNTY. 

vSome  of  the  American  Magnesite  Company’s  deposits  (see  p.  34) 
are  in  Stanislaus  County,  adjoining  the  Santa  Clara  County  line.  It 
is  probable  that  other  deposits  occur  along  the  western  edge  of  the 
county,  where  the  brushy,  sterile  hills  of  the  serpentine  area  are  but 
seldom  traversed. 


a Data  furnished  by  Chester  Naramore. 


38 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


SAN  BENITO  COUNTY. 

Extensive  areas  of  serpentine  occur  in  San  Benito  County,  in  which 
are  located  the  New  Idria  mercury  mines,  now  the  largest  producers 
in  California.  No  magnesite  has  been  reported,  but  it  is  probable 
that  it  may  yet  be  found.  At  present  transportation  facilities  are 
poor,  and  in  wet  weather  the  roads  are  very  bad. 

SAN  LUIS  OBISPO  COUNTY. 

Magnesite  in  small  veins  is  reported  to  occur  on  the  Kiser  place, 
8 to  9 miles  northwest  of  Cambria.  The  country  is  rough  and  the 
deposits  are  a long  way  from  railroad  transportation.  San  Simeon, 
a port  of  call  for  coastwise  vessels,  is  the  nearest  shipping  point. 

SANTA  BARBARA  COUNTY. 

Specimens  of  magnesite  seen  at  Santa  Barbara  were  said  to  come 
from  a deposit  about  20  miles  back  in  the  mountains.  No  details 
could  be  obtained,  but  the  specimens  seemed  to  indicate  that  they 
had  come  from  rather  small  veins.  As  a guide  could  not  be  obtained 
and  there  were  no  trails,  the  deposit  was  not  visited. 

RIVERSIDE  COUNTY. 

About  3£  miles  south  of  Winchester,  in  a hill  rising  about  650  feet 
above  the  surrounding  valley,  intrusives,  now  changed  largely  to  ser- 
pentine, have  been  thrust  into  biotite  schist  standing  on  edge  and 
having  a general  northwesterly  strike.  The  limits  of  the  serpenti- 
nous  bodies  are  rather  vague,  but  the  masses  are  probably  several 
hundred  feet  thick.  Pegmatite  dikes,  carrying  tourmaline,  cut  both 
schist  and  serpentine.  The  dikes  range  in  thickness  from  4 inches 
to  a number  of  feet,  and  where  they  cut  the  serpentine  chlorite  is 
developed  for  a distance  of  2 to  6 inches  on  each  side.  At  several 
places  along  the  schist-serpentine  contact  radial  asbestos  of  a poor 
quality  has  been  formed  through  a thickness  of  6 to  8 feet.  Narrow 
veins  of  fibrous  asbestos  are  developed  along  a vein  of  magnesite  a 
few  inches  thick  in  a tunnel  about  70  feet  long,  which  was  run  into 
the  hill  in  search  of  gold. 

At  a number  of  places  in  the  serpentine  trenches  have  been  dug 
exposing  magnesite  stockworks  with  veins  ranging  in  thickness  from 
2J  inches  down  to  those  too  small  to  be  readily  noticeable.  (See  PI. 
VIII,  A.)  From  the  best  exposure,  near  the  top  of  the  lull,  a piece 
of  magnesite  6 inches  thick,  18  inches  wide,  and  3 feet  long  was  said 
to  have  been  taken  out,  and  was  the  largest  piece  found.  In  general 
the  veins  at  this  point  are  from  one-half  inch  to  2 inches  thick,  with 
local  enlargements.  The  distance  between  veins  ranges  from  3 to  10 
inches.  The  magnesite  itself  is  spongy  and  porous. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  VIII 


A.  STOCKWORK  OF  MAGNESITE  VEINS  3£  MILES  SOUTH  OF  WINCHESTER. 


B.  SHEETED  SERPENTINE  CONTAINING  THIN  VEINS  OF  MAGNESITE,  NEAR  DEER 
CREEK,  TULARE  COUNTY. 


RIVERSIDE  AND  OTHER  COUNTIES. 


89 


A partial  analysis  of  the  magnesite  by  P.  H.  Bates,  of  the  United 
States  Geological  Survey,  is  as  follows : 

Partial  analysis  of  maynesite  from  hill  near  Winchester. 


Silica  (Si02) 4.73 

Alumina  (Al203) 12 

Ferric  oxide  (Fe203) 08 

Lime  (CaO) 43 

Magnesia  (MgO) 44.  77 

Carbon  dioxide  (C02) 49.40 


99.  53 

The  lime  is  fairly  low  and  there  is  little  iron,  but  the  silica  is  high. 
A company  has  been  formed  to  work  the  magnesite,  but  that  these 
deposits  can  compete  with  larger  ones  turning  out  as  good  or  better 
rock  in  other  parts  of  the  State  seems  doubtful. 

In  a well  bored  in  the  valley  about  a mile  northwest  of  this  deposit 
a magnesite  vein  20  inches  thick  is  said  to  have  been  struck.  It  was 
supposed  by  some  that  there  must  be  a connection  between  this  vein 
and  the  other  deposits,  but  there  is  no  ground  for  this  belief,  and 
such  a connection  is  altogether  unlikely. 

THE  SIERRA  NEVADA  OCCURRENCES. 

KERN  COUNTY. 

Magnesite  is  said  to  exist  in  Walkers  Pass,  in  the  Sierra  Nevada,  east 
of  Bakersfield,  but  the  deposits  are  so  far  from  railway  transportation 
that  they  are  not  now  of  economic  importance.  A specimen  seen  at 
Bakersfield  was  solid  and  of  good  white  color. 

TULARE  COUNTY. 

White  River  deposits.-— Ye  ins  reaching  6 inches  in  thickness  are  re- 
ported to  occur  along  White  River,  4 or  5 miles  west  of  Tailholt,  but 
none  of  workable  size  are  knowm. 

Deer  Creek  deposits. — On  and  near  the  top  of  a serpentine  hill  about 
1 mile  south  of  the  schoolhouse  at  Simmon’s  ranch,  about  8 miles 
southeast  of  Porterville,  there  are  a great  number  of  comparatively 
thin  veins  of  magnesite.  The  hill  is  a portion  of  the  outside  range 
of  foothills,  in  front  of  which  lie  two  or  three  smaller  hills,  also  of 
serpentinized  rock.  In  one,  directly  in  front  of  the  magnesite  de- 
posits and  about  1 mile  west,  chrysoprase  veins  are  being  mined.  A 
similar  occurrence  of  chrysoprase  veins  in  serpentine  containing  mag- 
nesite has  been  noted  at  Frankenstein,  Silesia.®  Veins  of  chalcedony 
up  to  3 inches  thick,  showing  greenish  tints,  occur  near  the  magnesite 
veins.  The  country  rock  is  a dull  brown  serpentinized  peridotite 


a Squire,  Lovell,  Some  observations  on  the  magnesite  of  Silesia:  Trans.  Royal  Geol.  Soc.  Cornwall, 
vol.  9,  pt.  1,  1875,  pp.  59-70. 


40 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


similar  to  that  near  Porterville.  (See  below.)  As  in  the  Porterville 
area,  the  rock  is  sheeted  in  places  and  contains  great  numbers  of  per- 
pendicular thin  parallel  veins  of  magnesite,  not  over  an  inch  thick 
and  about  an  inch  apart.  Crossing  the  perpendicular  veins  at  a 
small  angle  are  a second  series  of  veins,  and  a third  series  crosses  at 
right  angles.  (See  PL  VIII,  B.)  The  veins  are  probably  due  to 
shearing,  which  produced  cracks.  These  cracks  then  formed  chan- 
nels for  surface  waters,  and  were  filled  by  magnesite  derived  from  the 
decomposition  of  the  inclosing  rock  and  brought  by  the  waters  from 
a distance  and  precipitated.  Some,  but  not  many,  of  these  veins 
reach  2 feet  in  thickness  for  short  distances;  generally  they  are  dis- 
continuous and  irregular. 

A small  amount  of  magnesite  of  excellent  quality  has  been  mined 
on  the  west  side  of  the  hill  from  a nearly  vertical  vein  running  paral- 
lel to  the  course  of  the  hill  and  ranging  from  10  to  18  inches  in  thick- 
ness. 

A specimen  obtained  on  the  top  of  the  hill  was  partly  analyzed  by 
P.  H.  Bates,  of  the  United  States  Geological  Survey,  with  the  follow- 
ing result: 

Partial  analysis  of  magnesite  from  Deer  Creek , Tulare  County. 


Silica  (Si02)  - - - 0. 31 

Alumina  (A1203) 11 

Ferric  oxide  (Fe203) 08 

Lime  (CaO) 24 

Magnesia  (MgO) 47.  22 

Carbon  dioxide  (C02) 51. 64 


99.60  . 

This  is  an  excellent  magnesite,  the  total  impurities  amounting  to 
less  than  1|  per  cent,  but  on  the  other  hand  the  veins  are  small.  The 
deposit  is  not  more  than  3 or  4 miles  from  the  railroad,  and  may  at 
some  time  pay  to  work. 

On  the  east  side,  near  the  top  of  a somewhat  higher  hill  adjoining 
this  one  on  the  south,  other  small  deposits  of  magnesite  occur.  Sev- 
eral short  veins  up  to  2 feet  thick  were  seen.  Another  30  inches 
thick  is  said  to  be  located  not  far  from  the  saddle  between  the  hills. 

Porterville  deposits. — In  the  outer  range  of  foothills,  about  4 rniles 
northeast  of  Porterville,  magnesite  veins  stand  out  prominently  on 
two  rounded  hills  at  the  top  of  smooth,  steep  slopes,  rising  about 
1,000  feet  above  the  town.  One  of  the  hills,  which  will  be  referred 
to  as  the  northern  hill,  runs  a little  east  of  north,  and  the  other,  which 
will  be  referred  to  as  the  eastern  hill,  about  N.  60°  E.  At  their  junc- 
tion is  a saddle  about  300  feet  below  the  summits.  The  hills  are  free 
from  brush  or  trees,  and  the  broad  San  Joaquin  Valley  flattens 
smoothly  away,  so  that  the  white  veins  standing  above  the  surround- 
ing rocks  attract  attention  from  considerable  distances.  W.  P.  Blake, 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  IX 


A.  AMPHIBOLITE  DIKE  CUTTING  THROUGH  FLAT  VEIN  OF  MAGNESITE.  4 MILES  NORTHEAST 

OF  PORTERVILLE. 

Small  magnesite  veins  have  formed  in  the  amphibolite. 


B.  CRUSHED  MAGNESITE  VEIN,  2 FEET  WIDE,  NEAR  FURNACE  4 MILES  NORTHEAST  OF 

PORTERVILLE. 


TULARE  COUNTY. 


41 


who  passed  through  this  region  with  the  United  States  expeditions 
making  explorations  and  surveys  for  a railroad  in  1853,  briefly  de- 
scribed the  deposits  in  his  report.0  Mining  did  not  begin,  however, 
until  1901,  since  when  it  has  been  carried  on  continuously.  From 
1902  up  to  the  present  time  the  mining  has  been  done  by  the  Wil- 
lamette Pulp  and  Paper  Company,  which  controls  under  lease  the 
northern  hill  and  the  w^est  end  of  the  eastern  hill.  Charles  S.  Harker 
is  the  owner  of  both  hills  and  still  retains  control  of  the  larger  part 
of  the  eastern  hill.  The  veins  occur  in  a brown  serpentinized  perido- 
tite,  having  an  apparent  bedded' structure.  The  serpentine  forms 
part  of  a metamorphic  complex  consisting  of  a small  amount  of  fine- 
grained quartzite,  amphibolite  schist,  serpentine,  and  other  magnesian 
rocks,  some  of  which  are  talcose  and  mica  bearing.  The  rocks  have 
a general  northerly  strike,  with  a-  rather  high  (60°)  easterly  dip. 
They  are  cut  off  by  a granitic  mass  on  the  south,  a few  hundred  feet 
from  the  deposits.  (See  fig.  21.)  Several  granitic  dikes  cut  the  ser- 
pentine and  other  rocks,  but  do  not  cut  the  magnesite  veins,  though 
basic  dikes  (amphibolites)  of  several  varieties  cut  both  the  country 
rock  and  the  veins  and  are  here  and  there  squeezed  to  schist. 

Faulting  is  common,'  but  does  not  divide  the  serpentine  into  the 
small  irregular  blocks  which  result,  in  the  serpentines  of  the  Coast 
Range  and  many  others,  from  the  swelling  of  the  rock  as  it  changes 
its  chemical  and  mineralogical  form.  However,  movement  is  evi- 
dent, and  the  magnesite  is  invariably  crushed  in  the  larger  veins.  In 
one  vertical  2-foot  vein  a couple  of  hundred  feet  southeast  of  the 
kiln  (PI.  IX,  B)  the  magnesite  has  been  so  squeezed  that  it  is  left  in 
irregular  fragments  whose  sides  are  covered  with  abrasion  lines,  the 
whole  looking  as  if  at  the  time  of  crushing  it  had  been  in  a semi- 
plastic state.  In  other  veins  the  planes  along  which  the  magnesite 
has  moved  on  itself  are  smooth  and  shaped  so  as  to  somewhat  re- 
semble the  curve  of  a highly  arched  shell.  Along  many  of  these 
planes  is  a bright  red  stain  of  iron  oxide,  although  the  surrounding 
magnesite  is  pure  white.  In  other  places  the  magnesite  has  evidently 
been  crushed  almost  to  a powder  and  recemented. 

It  seems  probable  that  the  movements  which  have  caused  so 
much  crushing  and  distortion  have  been  due  to  other  causes  than 
the  serpen tinization  of  the  peridotite,  for,  as  stated,  it  is  not  badly 
shattered,  nor  does  it  show  the  great  number  of  smooth  faces,  due  to 
small  internal  movements,  that  are  common  under  such  circumstances. 
The  movements  here  may  have  been  due  to  the  stresses  occasioned 
by  the  raising  of  the  Sierra  Nevada,  to  the  intrusion  of  the  granite 
or  the  amphibolites,  or  to  all  of  these  causes. 


a Blake,  W.  P.,  Itinerary,  or  notes  and  general  observations  upon  the  geology,  mineralogy,  and 
agricultural  capabilities  of  the  route:  Report  of  explorations  in  California,  for  railroad  routes  to  con- 
nect with  the  routes  near  the  35th  and  32d  parallels  of  north  latitude,  Washington,  1856,  p.  28. 


42 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


Thin,  nearly  parallel  veins  of  magnesite,  mostly  but  a small  fraction 
of  an  inch  thick  and  hut  little  farther  apart,  occupy  zones  in  the 
serpentinized  rock  in  which  the  sheeting  due  to  shearing  and  crushing 
is  especially  prominent.  These  zones  are  practically  vertical.  The 
rocks  have  been  fissured  by  faulting  in  many  directions,  and  in  the 
fissures  magnesite  veins  have  been  deposited.  Two  of  the  largest 
veins  occupying  such  spaces  are  practically  flat.  The  veins  range 
in  thickness  from  threadlike  seams  to  8 feet,  and  the  principal  vein, 
which  occurs  in  the  northern  hill  (PI.  X,  A),  has  been  exploited 
through  the  hill,  a distance  of  785  feet,  and  can  probably  be  followed 
through  the  valley  between  the  hills  and  into  the  eastern  hill.  On  the 


Fig.  2. — Plan  of  magnesite  veins  and  workings  4 miles  northeast  of  Porterville,  Cal. 


northern  hill  this  vein  ranges  in  thickness  from  2 to  8 feet;  it  cuts 
the  lull  near  the  south  end  (see  PL  X,  A,  and  fig.  2),  strikes  north- 
west, and  dips  steeply  to  the  northeast.  An  amphibolite  dike  2 to  3 
feet  thick  has  been  intruded  into  the  serpentine  near  the  vein  and 
follows  it  for  a short  distance.  Along  this  stretch  the  vein  has  been 
squeezed  to  a schist;  at  other  places  it  is  comparatively  fresh. 
About  100  feet  from  the  southeastern  outcrop  of  the  vein  it  is  joined 
by  another  vein  of  about  the  same  thickness,  having  a strike  of 
N.  10°  W.,  which  has  also  been  mined. 

At  the  north  end  of  the  hill  are  two  “blanket”  or  flat  veins.  The 
largest  one  (PI.  X,  B)  is  practically  horizontal  in  the  middle  part  and 


NORTHERN  HILL  AT  WILLAMETTE  PULP  AND  PAPER  COMPANY’S  MAGNESITE  MINE  NEAR  PORTERVILLE,  LOOKING  NEARLY  NORTH. 
A,  Nearly  vertical  vein;  11,  Lower  " blanket  ” vein.  The  lower  line  ascending  toward  the  right  is  a tramway;  the  upper  one  is  a wagon  road. 


TULAKE  COUNTY. 


43 


somewhat  uplifted  at  both  ends — north  and  south.  It  extends 
through  the  hill,  a distance  of  362  feet,  and  is  probably  longer  than 
broad,  and  from  2 to  4 feet  or  more  thick.  A basic  dike  flattens  and 
spreads  under  a large  part  of  the  vein  in  a thin  sheet  1 to  2 feet 
thick;  then,  breaking  through  (PL  IX,  A),  it  overlies  the  remainder 
of  the  vein.  Thin  magnesite  veins  fill  cracks  in  the  dike,  but  the 
mass  of  the  vein  is  cut  by  it.  It  is  probable  that  small  veins,  similar 
to  those  in  the  dike,  are  being  formed  all  through  the  hill  at  the 
present  time.  There  is  nothing  to  show  that  the  vein  has  been  tilted 
from  a more  upright  position  to  its  present  place,  and  it  was  evidently 
formed  as  it  lies,  flat  and  cutting  across  the  vertical  structure  of  the 
serpentine.  This  is  accounted  for  by  supposing  that  there  was  a 
slow  movement  in  the  rocks  along  this  plane  at  the  time  of  the 
vein’s  deposition,  the  magnesite  filling  uneven  open  spaces  along 
the  horizontal  fault,  and  that  when  there  was  another  movement 
these  deposits  held  the  mass  apart  and  made  room  for  contiguous 
deposits.  The  crushed  condition  of  the  whole  mass  and  the  presence 
of  inclusions  of  serpentine  in  lines  approximately  parallel  to  the  sides 
of  the  vein  give  this  hypothesis  some  color. 

The  other  “ blanket”  vein  lies  above  the  north  end  of  the  vein 
just  described.  It  dips  at  a rather  low  angle  and  will  probably  be 
found  to  run  into  the  lower  one. 

Adjacent  to  all  the  larger  veins  are  many  small  reticulated  veins 
ranging  up  to  3 or  4 inches  in  thickness.  At  the  north  end  of  the 
deposits  is  a stockwork  of  small  veins  2 to  6 inches  thick  (PI.  XI,  A)f 
and  it  is  thought  that  it  may  pay  to  blast  the  whole  mass  and  hand 
pick  it.  Between  the  blanket  veins  and  the  large  vertical  vein  are  a 
number  of  smaller  veins,  from  the  outcrops  of  which  some  hundreds 
of  tons  of  magnesite  can  probably  be  broken.  At  the  north  end 
of  the  hill,  below  the  blanket  veins,  there  is  also  a considerable 
stockwork  of  veins  which  can  probably  be  worked  by  blasting  and 
hand  picking. 

On  the  west  end  of  the  eastern  hill  there  are  several  veins  of  magne- 
site reaching  a thickness  of  somewhat  more  than  3 feet,  from  which 
a small  amount  of  magnesite  has  been  mined. 

W.  P.  Bartlett,  the  superintendent  for  the  Willamette  Pulp  and 
Paper  Company,  has  developed  an  excellent  system  of  stoping  the 
vein  standing  at  a high  angle.  He  first  ran  a tunnel  through  the 
hill,  along  the  vein,  somewhat  less  than  100  feet  below  the  top. 
He  then  began  to  break  down  the  magnesite  from  the  roof  at  the 
farther  end  of  the  tunnel,  allowing  the  waste  to  accumulate,  so  that 
the  face  of  magnesite,  which  constantly  retreats  toward  the  portal  of 
the  tunnel,  could  be  reached  from  the  debris  slope,  down  which  the 
magnesite  was  rolled  and  removed  in  cars  from  the  foot.  This  proc- 
ess is  shown  diagrammatically  in  fig.  3.  The  magnesite  was  entirely 


44 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


removed  from  above  this  level,  and  the  same  system  is  being  worked 
on  the  level  below,  which  is  even  with  the  tramway,  and  when  this 
is  worked  out  probably  a still  lower  level  may  be  worked  on  the  same 
vein.  Either  underhand  or  overhand  stoping,  whichever  is  at  the 
time  more  advantageous,  can  be  carried  on  by  this  system. 

The  blanket  veins  require  the  removal  of  some  waste  rock,  as  the 
veins  are  not  thick  enough  (from  2 to  4 feet)  to  permit  economical 
working  by  mining  out  the  magnesite  alone.  The  waste  is  piled  in 
the  spaces  already  mined  and  forms  a partial  support  for  the  roof. 
The  roof  is  good  and  almost  no  timbering  is  required.  A small 
amount  of  work  has  been  done  on  some  of  the  smaller  veins,  both 
on  the  northern  hill  and  on  the  west  end  of  the  eastern  hill.  Practi- 
cally all  of  the  magnesite  mined  is  calcined,  and  a tramroad,  laid  on 
such  a grade  that  the  cars  run  down  by  gravity,  is  built  along  the 


Fig.  3. — Diagram  showing  mode  of  working  a highly  inclined  magnesite  vein  at  Willamette  Pulp  and 
Paper  Company’s  mine  near  Porterville,  Cal. 


east  side  of  the  northern  hill,  through  the  saddle,  to  the  kiln,  which 
is  located  near  the  west  base  of  the  eastern  hill.  The  veins  are 
fortunately  so  situated  that  the  tramway  runs  just  under  the  blanket 
veins  while  maintaining  its  grade  through  the  saddle.  The  kiln  is 
located  below  the  tramroad,  so  that  the  magnesite  is  dumped  into  a 
long  chute  through  which  it  slides  into  the  top  of  the  kiln.  (See 
PI.  XI,  B,  and  fig.  4.)  The  magnesite  is  broken  by  hand  at  the 
tunnels  to  lumps  4 inches  or  less  in  diameter.  Crude  oil  is  used 
for  fuel,  and  the  magnesite  gradually  rises  in  temperature  as  it  moves 
from  the  top  downward  through  the  kiln,  until  it  reaches  the  flame 
from  the  burners.  It  is  then  raised  to  a white  heat,  and  kept  there 
for  twenty  to  twenty-five  minutes,  when  it  is  withdrawn  from  below. 
It  is  said  that  after  this  treatment  3 to  5 per  cent  of  carbon  dioxide 
still  remains  in  the  material.  The  air  for  the  burners  passes  through 
the  withdrawn  material  and  is  thus  considerably  heated. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  XI 


A.  OUTCROP  OF  STOCKWORK  OF  VEINS  AT  NORTH  END  OF  WILLAMETTE  PULP  AND 
PAPER  COMPANY'S  DEPOSITS  NEAR  PORTERVILLE. 

Broken  magnesite  ready  for  calcining  in  foreground. 


B.  FURNACE  FOR  CALCINING  MAGNESITE  AT  WILLAMETTE  PULP  AND  PAPER  COMPANY’S 
MAGNESITE  MINE  NEAR  PORTERVILLE. 


TULARE  COUNTY. 


45 


Porterville,  Cal. 


46 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


The  following  analyses  of  magnesite  from  this  hill  are  at  hand: 


Analyses  of  magnesite  from  hill  4 miles  northeast  of  Porterville. 


1. 

2. 

Silica  (Si02> 

2.28 

0.90 

Altunina  (AI2O3) 

.03 

Ferric  oxide  ^Fe2Os) 

.26 

J-  .49 

Lime  (CaO) A. 'A 

1.32 

1.49 

44.39 

50.06 

Magnesia  (MgO) 

45. 17 

Carbon  dioxide  (CO2) 

50. 74 

Water  and  undetermined 

2. 57 

99.80 

99.90 

1.  Collected  by  the  writer  from  tunnel  No.  1 (in  the  large,  highly  inclined  vein),  and  analyzed  by 
A.  J.  Peters,  of  the  United  States  Geological  Survey. 

2.  Collected  by  W.  P.  Bartlett  and  analyzed  by  Abbot  A.  Hanks,  of  San  Francisco,  Cal. 


The  lime  in  these  samples  is  probably  too  high  to  allow  a good 
cement  to  be  made,  but  as  the  operating  company  uses  practically 
the  entire  product  in  wood-pulp  whitening  and  digestion  at  its 
Oregon  mills,  this  impurity  is  not  particularly  obnoxious. 

In  general  the  magnesite  is  white,  but  here  and  there  it  contains 
films  of  chlorite  or  serpentine  where  crushed.  At  other  places  there 
is  a red  stain  of  iron  oxide  on  the  surface  of  faces  that  have  slipped 
on  each  other.  Certain  faces  have  been  thinly  coated  with  quartz, 
and  one  such  face  in  which  shrinkage  cracks  affect  the  quartz  also  is 
shown  in  PI.  VI,  B. 

The  capacity  of  the  furnace  is  from  27  to  29  tons  of  magnesite  per 
day,  giving  13  to  14  tons  of  magnesia.  All  shipments  are  made  from 
Hilo  spur,  1 mile  north  of  the  Porterville  station. 

On  the  eastern  hill  there  are  a large  number  of  magnesite  veins  of 
dimensions  similar  (except  in  length,  in  which  they  are  probably 
deficient)  to  those  on  the  northern  hill.  The  total  amount  of  mag- 
nesite is  probably  considerably  less;  as  already  stated,  one  vein  may 
be  the  extension  of  the  main  vein  cutting  the  northern  hill.  No  such 
flat  veins  as  those  described  on  the  northern  hill  are  to  be  seen  here. 
In  places  the  veins  contain  a considerable  amount  of  serpentine  in 
fine  particles,  and  elsewhere  the  serpentine  contains  sufficient  mag- 
nesite to  give  it  a gray  appearance. 

A small  amount  of  magnesite  has  been  removed  by  open  excava- 
tions and  shipped  by  Charles  S.  Harker,  the  owner,  to  Oakland  for 
the  manufacture  of  carbon  dioxide. 

Deposits  on  South  Fork  of  Tule  River. — In  a high  hill  on  the  south- 
west side  of  South  Fork  of  Tule  lliver  are  a large  number  of  magnesite 
veins  with  outcrops  ranging  in  thickness  up  to  20  feet.  The  mag- 
nesite veins  seen  are  on  the  north  side  of  the  hill  in  secs.  30  and  31, 
T.  22  S.,  R.  29  E.  They  are  less  than  a mile  south  of  Success  school- 
house  and  about  9 miles  from  the  railroad  at  Porterville.  Should 


TULARE  COUNTY. 


47 


active  work  be  undertaken,  the  road  could  probably  be  somewhat 
shortened.  The  haul  is  almost  entirely  down  hill.  An  electric  road 
from  Porterville  to  Springville,  which  has  been  under  contemplation 
for  some  time,  if  built,  would  pass  within  3 miles  of  the  deposits. 

As  Success  schoolhouse  is  the  most  readily  identifiable  object  in 
the  landscape,  the  directions  used  in  this  description  will  be  given 
with  reference  to  it. 

The  portions  of  the  hill  containing  the  magnesite  are  composed  of 
a rock  much  more  completely  serpentinized  than  that  nearer  Porter- 
ville. In  the  sections  examined  there  are  only  scattered  fragments 
of  original  minerals,  probably  pyroxenes,  locally  in  radial  crystals, 
which,  in  the  hand  specimen,  reach  2 inches  in  length. 

At  the  foot  of  the  hill  S.  26°  W.  (magnetic)  from  Success  school- 
house,  a magnesite  vein  outcrops  along  the  edge  of  the  narrow  flood 
plain  of  the  river.  The  outcrop  is  from  3 to  10  feet  thick,  and  is 
exposed  prominently  for  a distance  of  about  500  feet,  running  north- 
westward, parallel  to  the  river.  In  this  distance  it  rises  from  the 
level  of  the  flood  plain  to  60  feet  above  it  at  the  southeast  end.  What 
is  apparently  the  end  of  the  outcrop,  however,  may  be  only  the  point 
to  which  it  has  been  covered  by  debris  from  the  hill  slope,  and  at 
the  other  end  it  may  run  for  some  distance  beneath  the  covering 
of  soil.  At  each  end,  however,  is  a small  watercourse,  and  in  ser- 
pentine areas  such  channels  very  commonly  mark  fault  lines.  The 
magnesite  is  generally  of  a good  white  color,  but  is  here  and  there 
grayish.  In  places  the  vein  contains  horses  of  serpentine,  and  at 
one  place  it  is  cut  by  a fine-grained  basic  dike,  which  is  composed 
mainly  of  light-green  amphibole  and  a fresh  plagioclase  feldspar  with 
much  magnetite,  and  which  for  most  of  the  distance  that  it  is  visible 
runs  approximately  parallel  to  the  vein. 

On  the  assumptions  that  5 feet  is  the  average  thickness  of  the  vein 
and  that  it  extends  for  100  feet  into  the  hill — both  of  which  premises 
seem  wholly  reasonable — the  vein  would  contain  500  (length)  X 5 
(thickness)  X100  (depth)  =250,000  cubic  feet,  which,  on  the  basis  of 
11  cubic  feet  per  short  ton,  is  equivalent  to  about  22,700  tons. 

A partial  analysis  of  magnesite  from  this  vein,  made  by  A.  J.  Peters, 
gave  the  following  result: 

Analysis  of  magnesite  from  hill  south  of  Success  schoolhouse,  Tulare  County. 


Silica  (Si02) 0.80 

Alumina  ( A1203) 42 

Ferric  oxide  (Fe203) 20 

Lime  (CaO) 1.02 

Magnesia  (MgO) 45.94 

Carbon  dioxide  (C02) 51.30 


99.68 


48 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


The  total  impurities  here  amount  to  nearly  2.5  per  cent,  of  which 
about  1 per  cent  is  lime.  There  is  probably  enough  lime  to  make  it 
undesirable  for  the  manufacture  of  cement,  but  it  is  a good  material 
for  use  in  paper,  gas,  or  brick  making. 

* The  serpentine  is  in  places  full  of  thin  parallel  veins  of  magnesite, 
similar  to  those  at  the  deposits  near  Porterville  and  Deer  Creek.  A 
couple  of  hundred  feet  above  and  west  of  the  northwest  end  of  the 
large  vein  just  described  are  a large  number  of  irregular  magnesite 
nodules  and  masses,  from  which  probably  several  hundred  tons  could 
be  blasted  at  small  cost.  In  the  same  neighborhood  there  are  a num- 
ber of  smaller  veins.  About  200  feet  (barometric  measurement) 
above  the  flat  vein  is  a fairly  continuous  outcrop  reaching  possibly  20 
feet  in  thickness  and  200  feet  in  length,  in  which  the  magnesite  is  of  a 
beautiful  pure-white  color,  but  there  are  many  inclusions  of  serpentine. 

At  a point  S.  17°  W.  (magnetic)  of  Success  schoolhouse  and  about 
800  feet  (barometric)  above  the  river  is  a vein  from  2 to  6 feet  wide, 
which  may  be  followed  for  about  200  feet.  The  strike  is  northwest- 
ward, with  a high  northeasterly  dip. 

On  the  top  of  the  hill,  at  an  altitude  of  over  1,000  feet  above  the 
river,  are  a number  of  veins  ranging  up  to  6 feet  in  thickness,  but  most 
of  them  can  not  be  traced  far.  One  vein,  averaging  between  2 and  3 
feet  in  thickness,  was  followed  for  250  feet,  and  with  greater  care  it 
may  be  possible  to  trace  it  farther.  These  veins  are  nearly  a mile 
south  of  the  flat  vein  first  described,  and  in  the  intervening  space  are 
hundreds  of  irregular  veins,  which  measure  up  to  a foot  or  even  more 
in  thickness  and  which,  in  places  near  the  river,  form  stockworks  that 
could  be  blasted  and  hand  picked  at  small  expense. 

The  belt  of  serpentine  carrying  the  magnesite  has  been  crushed  and 
sheeted  in  a northwesterly  direction,  and  probably  owes  this  structure 
to  the  forces  that  acted  similarly  on  the  magnesite-bearing  serpentines 
nearer  Porterville,  which  lie  about  6 miles  northwest.  No  develop- 
ment work  has  been  done  on  these  deposits.  ° 

Round  Valley  deposits. — On  the  east  side  of  the  mouth  of  Pound 
Valley,  between  3 and  4 miles  east  of  Lindsay,  a number  of  magnesite 
veins  ranging  up  to  2 feet  in  thickness  crop  out  on  the  southwestern 
face  of  the  hill,  between  150  and  450  feet  (barometric)  above  the  floor 
of  the  valley.  The  country  rock  is  serpentine,  similar  in  macroscopic 
appearance  to  that  at  Porterville.  The  belt  in  which  the  veins  occur 
has  a northwestern  trend  similar  to  that  of  the  deposits  on  South  Fork 
of  the  Tule  and  of  those  near  Porterville.  The  lower  veins  are  of  poor 
quality,  as  they  contain  a considerable  amount  of  serpentine.  The 
upper  veins  appear  to  be  of  good  quality,  but  all  are  thin  and  too  far 


a Since  this  paper  went  to  press  word  has  been  received  from  Mr.  W.  P.  Bartlett  that  he  is  now 
shipping  magnesite  from  these  deposits. 


TULARE  COUNTY. 


49 


apart  to  be  worked  economically  from  the  same  opening.  Hauling  to 
the  Southern  Pacific  Railroad  at  Lindsay  would  be  easy  and  on  down 
grade  all  the  way. 

Deposits  near  Exeter. — Magnesite  had  been  reported  to  the  writer 
as  occurring  in  a number  of  the  orange  orchards  east  of  Exeter,  where 
it  was  said  to  be  killing  the  trees,  but  in  each  case  the  substance  was 
found  to  be  carbonate  of  lime.  However,  on  the  southwest  spur  of 
Rocky  Hill,  2 miles  east  of  Exeter,  there  are  a few  small  veins  of 
magnesite  about  500  feet  above  the  valley.  The  largest  vein  is  not 
more  than  a foot  wide,  and  most  of  them  are  only  from  1 to  3 inches 
wide.  The  area  over  which  the  veins  occur  is  very  small  and  the 
deposits  are  without  economic  value. 

A vein  of  califomite,  a variety  of  vesuvianite,  occurs  alongside  the 
magnesite.  It  is  said  to  have  been  worked  under  the  supposition  that 
it  was  impure  chrysoprase.  From  the  matter  thrown  out  the  vein 
appears  to  be  from  2 to  4 inches  wide.  The  rock  in  the  shaft  was  so 
much  shattered  and  coated  with  calcareous  material  that  the  vein 
could  be  but  imperfectly  made  out.  The  color  of  the  califomite  is 
rather  irregular;  the  ground  color  is  a light  green,  carrying  a hint  of 
yellow,  but  through  this  are  sprinkled  small  spots  of  buff  or  white,  and 
spots  about  one  sixty-fourth  of  an  inch  across  of  dark  green. 

Deposits  of  magnesite  were  reported  in  the  Yokohl  Valley,  a few 
miles  east  or  southeast  of  Exeter,  but  they  could  not  be  definitely 
located. 

Naranjo  deposits. — George  D.  Ward,  of  Oakland,  is  interested  in 
some  small  deposits  of  magnesite  about  7 miles  northwest  of  Lemon 
Cove  and  1 mile  northwest  of  Naranjo  post-office.  The  deposits  are 
situated  in  a serpentine  hill  containing  many  intrusions  of  greenstone 
and  granite.  Most  of  the  veins  are  from  2 to  5 inches  thick  and  are 
exposed  for  only  a few  feet.  They  are  in  general  of  rather  pure- 
looking  but  spongy  material  though  some  have  considerable  serpentine 
mixed  with  them.  The  largest  vein  is  situated  on  the  north  side  of 
the  hill  and  is  but  16  inches  thick.  A small  excavation  has  been  made, 
and  this  affords  the  only  exposure.  The  vein  is  much  crushed  and 
the  magnesite  appears  to  be  of  only  fair  quality.  At  a number  of 
places  on  the  hill  are  veins,  1 to  2 inches  thick,  of  translucent  white 
nonprecious  opal. 

Other  Tulare  County  deposits. — Small  veins  of  magnesite  are  reported 
to  occur  near  Auckland,  but  they  are  probably  of  little  importance. 
There  are  undoubtedly  other  veins,  which  may  or  may  not  be  of 
value,  in  the  great  areas  of  serpentine  that  lie  along  the  foothills  of  the 
Sierra  Nevada  through  the  entire  length  of  the  county. 

51136— Bull.  355—08 4 


50 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


FRESNO  COUNTY. 

Nine  miles  east  of  Sanger  George  D.  Ward  has  located  magnesite 
claims  on  both  sides  of  Kings  River,  near  what  is  known  as  Red  Hill. 
The  country  is  one  of  rather  high,  smooth,  nearly  treeless  hills,  rising 
perhaps  somewhat  over  1,000  feet  above  the  river.  The  rocks  are 
metamorphic  and  include  some  serpentine  and  partially  serpentinized 
tuff.  They  are  all  in  comparatively  narrow  bands,  and,  except  the 
serpentine,  are  gneissoid.  Much  of  the  rock  was  originally  granite  or 
diorite.  All  the  rocks  have  a structure  much  resembling  bedding. 
The  amount  of  magnesite  in  sight  seems,  at  first  glance,  remarkably 
large  for  the  amount  of  serpentine  present. 

On  the  north  side  of  the  river  the  principal  vein  is  on  what  is 
known  as  the  Snow  Cap  claim.  The  vein  outcrops  about  half  a mile 
from  the  river,  in  a small  embayment  in  the  hills.  A face  has  been 
exposed  showing  the  magnesite  to  be  at  least  8 feet  thick.  (See  PL 
XII,  B.)  It  has  a strike  of  N.  24°  W.  (magnetic)  and  an  easterly  dip 
of  about  75°,  which  probably  agree  with  the  strike  and  dip  of  the 
country  rocks.  On  the  foot  wall  is  a considerable  amount  of  soft, 
friable  magnesite,  which  is  very  much  like  calcareous  tufa  and  which 
is,  in  fact,  a magnesian  tufa.  This  deposit  is  more  than  a foot  thick. 
About  3 feet  from  the  foot  wall  is  an  irregular  vein  of  magnesite, 
from  6 inches  to  3 feet  thick,  which  probably  joins  the  main  vein  a 
short  distance  below,  and  which  could  be  economically  mined  with  it. 
The  vein  can  be  definitely  followed  for  about  600  feet  to  the  north, 
across  a low  hill,  and  seems  to  get  thinner  toward  the  farther  end. 
The  magnesite  is  a clear  white,  containing  serpentine  only  here  and 
there. 

A partial  analysis  of  a specimen  of  fine-grained  pure-white  mag- 
nesite from  the  body  of  the  vein,  collected  by  the  writer  and  analyzed 
by  A.  J.  Peters,  was  as  follows: 

Analysis  of  magnesite  from  large  vein,  Snow  Cap  claim,  Kings  River. 


Silica  (Si02) 0.20 

Alumina  ( A1203) 04 

Ferric  oxide  (Fe203) 12 

Lime  (CaO) 96 

Magnesia  (MgO) 46.48 

Carbon  dioxide  (C02) 51.80 


99. 60 

It  will  be  noticed  that  there  is  nearly  1 per  cent  of  lime  in  the 
specimen,  although  a commercial  analysis  made  for  Mr.  Ward  was 
said  to  show  none. 

A quarter  of  a mile  north  from  the  end  of  the  vein,  along  the  same 
strike,  is  a vein  of  rather  impure  magnesite.  The  dip  is  shallower 
and  it  is  not  likely  that  the  two  veins  are  connected. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  355  PL.  XII 


A.  MAGNESITE  VEIN  ON  SOUTH  SIDE  OF  KINGS  RIVER,  9 MILES  EAST  OF  SANGER. 


B.  MAGNESITE  VEIN  ON  SNOW  CAP  CLAIM,  NORTH  SIDE  OF  KINGS  RIVER,  9 MILES  EAST 

OF  SANGER. 


/, 


FRESNO  AND  OTHER  COUNTIES. 


51 


A couple  of  hundred  feet  up  the  ridge,  west  from  the  main  outcrop 
of  the  Snow  Cap,  is  a magnesite  vein  of  good  quality  from  10  to  21 
inches  wide,  which  may  be  followed  for  100  to  150  feet.  It  is  on  the 
Snow  Cap  claim.  On  the  same  claim,  in  the  gulch  on  the  south, 
200  feet  from  the  main  outcrop  of  the  Snow  Cap  and  just  below  an 
old  wagon  road,  a mass  of  fine  white  magnesite  showing  a surface  of 
8 by  13  feet  has  been  uncovered.  At  the  time  of  visit  not  enough 
work  had  been  done  to  show  whether  the  occurrence  was  a vein  or  a 
large  nodule. 

On  the  Governor  claim,  a quarter  of  a mile  S.  16°  W.  from  the 
main  Snow 'Cap  outcrop,  across  a gulch  and  about  100  feet  (baro- 
metric measurement)  above  the  Snow  Cap,  is  a small  outcrop  of  a 
magnesite  vein  of  good  quality,  dipping  highly  S.  60°  E.  It  is  prob- 
ably 2 feet  thick  and  has  been  exposed-  for  a length  of  10  feet.  Mag- 
nesite float,  which  has  been  found  300  feet  or  more  to  the  southwest, 
has  been  supposed  to  come  from  the  extension  of  this  vein,  but  there 
is  nothing  at  present  shown  to  prove  it. 

Besides  the  vein  mentioned  there  are  at  a number  of  places  smaller 
veins,  largely  of  noncompact  magnesite.  The  surfaces  of  the  spongy 
magnesite  are  colored  a fine  pink.  Small  red  lichens  grow  upon  the 
magnesian  rocks  of  this  vicinity,  and  if  treated  with  an  alkali  (sodium 
hydrate  or  ammonia)  they  give  the  same  pink  hue,  so  that  the  color 
may  be  derived  from  these  lichens,  or  it  may  be  due  to  some  iron 
compound.  No  other  coloring  material,  such  as  cobalt  or  manganese, 
which  would  account  for  it  could  be  detected  in  the  specimens. 

On  the  south  side  of  Kings  River,  about  half  a mile  from  and  650 
feet  above  the  stream,  is  a fine  large  vein  of  magnesite,  which  runs 
east  and  west  across  a northward-projecting  hill.  (See  PI.  XII,  A.) 
The  vein  as  exposed  at  the  time  it  was  visited  was  at  least  8 feet  wide 
and  may  have  been  somewhat  wider.  It  could  be  readily  traced  for 
about  200  feet,  but  no  attempt  had  been  made  to  show  its  length  by 
excavations,  so  that  it  may  prove  to  extend  farther.  The  magnesite 
seemed  to  be  of  good  quality,  with  but  few  inclusions  of  serpentine. 

The  deposit  is  reached  by  a fairly  easy  grade  and  could  be  very 
economically  worked.  The  haul  from  the  deposits  on  both  sides  of 
the  river  to  the  railroad  at  Sanger  is  all  downhill  except  for  trifling 
grades,  and  in  general  the  roads  are  excellent.  The  magnesite  from 
the  two  sides  would,  however,  have  to  go  by  different  roads,  owing 
to  the  difficulty  of  fording  the  river. 

MARIPOSA  AND  TUOLUMNE  COUNTIES. 

Large  bodies  of  magnesite  containing  green  mica  and  pyrite  have 
occasionally  been  reported  from  Mariposa  and  Tuolumne  counties,  but 
probably  most  if  not  all  of  the  deposits  referred  to  are  dolomite  con- 


52 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


taming  large  amounts  of  mariposite,  a chrome  mica.  There  are  in 
these  counties,  however,  belts  of  serpentine  in  which  it  would  not  be 
surprising  to  find  magnesite,  though  the  writer’s  inquiries  have  so  far 
located  none. 

PLACER  COUNTY. 

Damascus  deposits. — Many  statements  have  been  published  from 
time  to  time  heralding  the  deposits  near  Damascus  as  “the  largest  in 
the  State,”  possibly  because  they  are  among  the  least  convenient  to 
reach.  The  writer  did  not  visit  the  locality,  as  at  the  time  he  was  in 
this  portion  of  the  State  the  deposits  were  reported  to  be  covered  with 
snow.  The  magnesite  is  in  the  S.  \ sec.  18,  T.  15  N.,  R.  11  E.,  3 or 
4 miles  from  Damascus  and  Michigan  Bluff  and  probably  not  more 
than  10  miles  in  a direct  line  from  Colfax.  The  following  inf ormation 
was  kindly  furnished  by  Mr.  Harold  T.  Power,  of  Bullion,  Cal.,  and 
Mr.  H.  W.  Turner,  formerly  of  the  United  States  Geological  Survey, 
but  now  of  Portland,  Oreg. 

In  the  southwest  quarter  of  the  section  the  deposits  are  located 
just  below  the  Morning  Star  ditch,  in  a serpentine  country  rock. 
Besides  a number  of  small  veins  an  inch  or  so  in  width,  there  are  sev- 
eral lenses  of  magnesite  forming  practically  one  body  about  30  feet 
in  width  and  100  feet  long,  which  contains  some  serpentine.  A spec- 
imen sent  in  by  Mr.  Power  is  of  good  appearance,  though  not  very 
compact.  As  no  analysis  has  been  made,  its  composition  can  not  be 
given.  A small  exposure  of  a 2-foot  vein  is  said  to  occur  in  the 
southeast  quarter  of  the  section. 

The  country  is  so  rough  that  under  present  conditions  the  mag- 
nesite can  not  be  mined  at  a profit.  A lumber  railroad  has  been 
surveyed  to  run  close  to  the  deposits,  and  should  such  a road  be 
built  they  might  be  worked. 

W.  P.  Bartlett,  of  Porterville,  reports  a 2-foot  vein  of  magnesite  in 
the  canyon  of  American  River,  near  this  place,  but  on  account  of  its 
unfavorable  location  it  is  valueless.  Other  small  veins  also  have 
been  reported,  but  so  far  nothing  of  value  has  been  found. 

MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 

It  is  always  desirable  to  know  something  of  mineral  deposits  which 
may  be  possible  or  certain  competitors  in  any  mining  or  quarrying 
enterprise.  California’s  commercial  isolation  from  the  eastern  portion 
of  the  United  States,  caused  by  the  long  railroad  hauls,  precludes 
railroad  shipment  of  products  that  sell  as  cheaply  as  magnesite. 
Owing,  however,  to  the  possibility  of  shipping  by  water  with  a fair 
margin  of  profit,  the  following  notes  on  competing  foreign  deposits  are 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


53 


NORTH  AMERICA. 

CANADA. 

Quebec. — Magnesite  occurs  at  a number  of  places  in  the  Dominion 
of  Canada,  but  the  deposits  known  seem  to  be  remarkably  different 
from  those  of  California.  In  eastern  Canada  magnesite  has  been 
found  in  the  township  of  Grenville,  Argenteuil  County,  Quebec,®  in 
place  and  in  loose  bowlders,  some  of  the  latter  weighing  many  tons. 
In  appearance  this  magnesite  is  granular  and  much  like  clear,  rather 
coarse  grained  marble,  and  it  is  supposed  to  be  of  sedimentary  origin. 
One  outcrop  is  about  100  feet  wide  and  a quarter  of  a mile  long.  If  it 
is  a sedimentary  deposit  it  is  unique,  so  far  as  has  come  to  the  atten- 
tion of  the  writer,  as  nowhere  else  are  magnesian  sediments  known  in 
which  the  percentage  of  magnesium  carbonate  present  exceeds  to  any 
appreciable  degree  the  theoretical  amount  contained  in  dolomite 
(45.65  per  cent).  Although  limestones  carrying  any  percentage  of 
magnesium  carbonate  up  to  45.65  may  be  found,  the  remainder  of  the 
series  between  45.65  and  100  per  cent  have  had  no  representatives 
until  the  discovery  of  these  deposits.  Analyses  by  the  Geological 
Survey  of  Canada  of  various  specimens  showed  magnesium  carbonate, 
49.71  to  95.50  per  cent;  calcium  carbonate  from  a “very  small 
amount”  to  30.14  per  cent;  and  magnesia  other  than  carbonate 
(probably  nearly  all  serpentine),  3.08  to  9.17  per  cent. 

An  average  of  57  samples  from  another  locality  gave — 

Average  composition  of  magnesite  from  Quebec. 


Magnesium  carbonate 81.  27 

Calcium  carbonate 13. 64 

Magnesia  other  than  that  present  as  carbonate 3.  66 


98.57 


British  Columbia. — In  the  Atlin  district  of  British  Columbia,  at  the 
town  of  Atlin, h deposits  of  hydromagnesite  (3  MgC03.Mg  (HO)2  + 3H20) 
occur  in  Pine  Creek  valley  as  a line  white  powder  covering  several 
acres  and  known  to  be  as  much  as  5 feet  deep.  The  deposits  are 
evidently  derived  from  springs,  the  waters  from  which  carry  1.834 
parts  of  magnesia  in  1,000.  Hydromagnesite  when  pure  carries  43.9 
per  cent  of  magnesia,  36.3  per  cent  of  carbon  dioxide,  and  19.8  per 
cent  of  water. 

Similar  deposits0  occur  at  the  108-mile  House  on  the  Cariboo  road 


a Hoffman,  G.  C.,  Report  of  the  section  of  chemistry  and  mineralogy:  Ann.  Rept.  Geol.  Survey 
Canada,  vol.  13  (for  1900),  pt.  R,  1903,  pp.  14-19. 

6 Gwillim,  J.  C.,  Report  on  the  Atlin  mining  district,  British  Columbia:  Ann.  Rept.  Geol.  Survey 
Canada,  vol.  12,  pt.  B,  1899,  pp.  47-48. 

c Hoffman,  G.  C.,  Report  of  section  of  chemistry  and  mineralogy:  Arm.  Rept.  Geol.  Survey  Canada, 
vol’.  11, 1900,  pp.  10-11. 


54 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


93  miles  north  of  Ashcroft,  Lillooet  district,  British  Columbia,  where 
they  are  scattered  over  50  acres  or  more  of  ground.  At  three  or  four 
places  patches  of  the  material  50  to  100  feet  wide  stand  afoot  or  more 
above  the  general  surface.  At  one  point  a shaft  showed  the  deposit 
to  be  over  30  feet  thick. 

At  Atlin  an  exceedingly  impure  magnesite  occurs  with  serpentine 
and  dunite,a  and  is  said  to  be  over  1,000  feet  wide  on  the  Anaconda 
group  of  claims.  It  is  impregnated  with  iron  pyrites,  and  is  cut  by 
apple-green  quartz  carrying  1 pennyweight  of  gold  per  long  ton  and 
15  per  cent  of  nickel.  A partial  analysis  of  the  magnesite  is  as 
follows : 

Partial  analysis  of  magnesite  from  Atlin,  British  Columbia. 


Magnesia  (MgO) 21. 70 

Protoxide  of  iron  (Fe203) 5. 10 

Carbonic  acid  (C02) 27. 00 

Silica  (Si02) 45. 68 

Combined  water  and  loss 0.  52 


100. 00 

Under  present  conditions  these  British  Columbia  deposits  are 
probably  without  economic  value. 

MEXICO. 

Lower  California. — On  the  island  of  Santa  Margarita,  in  Magdalena 
Bay,  extensive  deposits  of  magnesite  have  recently  been  examined  by 
Julius  Koebig,  of  Los  Angeles,  for  a firm  of  that  city.  The  country 
rocks  are  said  to  be  sandstone,  quartzite,  and  syenite.  No  mention  is 
made  of  more  magnesian  rocks,  though  it  seems  highly  probable  from 
the  amount  of  magnesite  described  that  such  rocks  are  present.  The 
island  is  mountainous  and  is  25  miles  long  by  4 or  5 miles  broad. 
Doctor  Koebig  says  in  his  report : 

Practically  every  canyon  of  the  Sienite  Mountains,  by  decomposition  of  the  eruptive 
rocks,  shows  larger  or  smaller  deposits  covering  in  some  instances  the  entire  surface  of 
hills  and  mountain  sides.  The  banks  of  the  canyons,  where  the  rocks  have  been  cut 
by  the  streams  during  the  rainy  season,  show  magnesite  strata  several  feet  thick,  and 
for  a distance  of  a few  hundred  feet  to  over  a mile  the  arroyo  itself  contains  large  quan- 
tities of  magnesite  in  the  shape  of  bowlders,  weighing  from  a few  pounds  to  3 to  5 tons 
apiece.  * * * Estimated  in  the  most  conservative  way,  I have  seen  actually  in 
sight  on  the  surface,  and  in  no  case  more  than  H miles  from  shore,  300,000  to  500,000  tons 
ready  to  be  picked  up  and  packed  to  the  beach  without  the  use  of  any  tools  other  than 
a sledge  hammer.  * * * For  labor  there  are  plenty  of  Mexicans  to  be  had  at  not 
to  exceed  $1.50  Mexican  per  day.  * * * As  means  of  transportation  to  the  wharf 
there  are  300  or  more  donkeys  on  the  island.  * * * There  is  plenty  of  water  for  a 
crew  of  Mexicans  and  the  pack  animals. 


a Gwillim,  J.  C.,  op.  cit.,  pp.  21-22. 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


55 


The  following  analyses  are  given  in  the  report : 

Analyses  of  magnesite  from  Santa  Margarita  Island , Lower  California. 


1. 

2. 

Insoluble,  sand  and  clay 

Trace. 
} 0.21 
.43 

0.06 

.10 

Trace. 

Ferric  oxide  (Fe203> 

Alumina  (AI2O3) 

Carbonate  of  lime  (CaCOs) 

Lime  (CaO) 

Carbonate  of  magnesia  (MgCOs) 

99. 36 

Magnesia  (MgO) 

99.05 

1.  Raw  magnesite;  analyst  unknown. 

2.  Calcined  magnesite;  analysts,  Baverstock  & Staples,  Los  Angeles,  September  13, 1907. 


The  company  offers  to  furnish  the  magnesite  for  $3.50  f.  o.  b.  vessel 
at  Santa  Margarita. 

Other  deposits  of  magnesite  are  reported  from  various  parts  of  Mex- 
ico, but  little  is  known  of  them. 

SOUTH  AMERICA. 

VENEZUELA. 

The  Venezuelan  Government  has  recently  granted  for  twenty-five 
years  the  exclusive  privilege  a of  exporting  magnesite  found  on  private 
lands  on  the  island  of  Margarita,  to  a company  which  expects  to  ship 
from  12,000  to  15,000  tons  annually.  Nothing  further  is  known  of 
the  deposits. 

Dana6  quotes  N.  S.  Manross  as  stating  that  magnesite  occurs  near 
Mission  Pastora,  in  Canton  Upata. 

EUROPE. 

AUSTRIA. 

Styria  in  Austria  has  very  large  deposits  of  magnesite  which  are 
actively  worked.  The  largest  company  is  the  Veitscher  Magnesit- 
werke  Actiengesellschaft,c  with  mines  at  Veitsch,  5 miles  from  the 
Mittersdorf  Murzthal  railway  station.  During  1903  this  company 
produced  71,016  tons  of  magnesite  and  shipped  to  the  United  States 
35,000  tons  of  the  calcined  product. 

This  company  and  the  Magnesite  Company,  Limited,  of  Hungary, 
have  a working  agreement. d 

a Moffat,  T.  P.,  Daily  Consular  and  Trade  Repts.,  No.  3108,  Washington,  February  25, 1908,  p.  8. 
&Dana,  E.  S.,  Descriptive  mineralogy,  6th  ed.,  New  York,  p.  275. 
c Rublee,  W.  A.,  Daily  Consular  Repts.,  No.  2276,  Washington,  June  6,  1905,  p.  2. 
d Private  letter. 


56 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


HUNGARY. 

The  Magnesite  Company,  Limited,®  with  headquarters  at  Nyustya, 
Gomor  County,  is  the  largest  company  operating  in  Hungary.  The 
veins  worked  are  very  large,  ranging  from  150  to  300  feet  in  width, 
and  are  worked  as  open  quarries,  with  stages  from  40  to  60  feet  high. 
The  magnesite  is  yellowish  or  bluish  white,  in  some  places  fine  grained 
and  in  others  of  very  coarse  crystalline  structure.  The  following 
analyses  of  the  magnesite,  of  which  No.  2 is  calcined,  are  given  as 
representative : 

Analyses  of  Nyustya  magnesite. 


1. 

2. 

Silica  (Si02) . 

0.  74-  0.  76 
.39-  .27 
3.  27-  3.  43 
1.20-  .90 
44.  80-45.  00 
50. 10-50.  20 

1.67 
3.  47 

4.68 
2.  94 

86.90 

Alumina  (AI2O3) 

Ferric  oxide  (Fe203) 

Lime  (CaO) 

Magnesia  (MgO) . ... . 

Carbon  dioxide  (CO2) 

The  output  of  dead-burned  magnesite  of  the  company  in  1904 
(1905?)  was  22,000  to  23,000  tons  from  Nyustya  and  11,000  to  12,000 
tons  from  Jolsva  and  Ochtina.  The  company  was  at  that  time  mak- 
ing 750,000  magnesite  brick  per  year. 

The  production  of  magnesite  in  Hungary  during  1907  was  as  fol- 
lows:6 

Production  of  magnesite  in  Hungary,  1907. 


Quantity. 

Value. 

United  Magnesite  Company,  Nyustya 

Quintals. 

98,000 

1,090 

1,126 

Crowns. 

519,000 

1 

Company  of  Magnesite-Industry: 

Nyustya  (Gomor) 

Jolsva  (Gomor) 

1 10,877 

Martonbaza * 

437 

General  Magnesite  Company,  Hizsnyo  (Gomor) 

78,000 

330,000 

178,653 

859,877 

The  product  is  equivalent  to  19,693  short  tons,  valued  at  $174,554. 
The  whole  output  was  made  into  brick. 

Besides  brick  and  calcined  magnesite,  the  Hungarian  companies 
ordinarily  make  “ caustic”  or  partly  calcined  magnesite  for  use  as  a 
mortar,  with  which  magnesite  brick  are  set. 

GERMANY. 

Deposits  of  magnesite  were  worked  for  many  years  in  the  neighbor- 
hood of  Frankenstein,  Silesia.0  The  magnesite  is  said  to  occur  in 

a Private  letter. 

b Letter  from  director  substitute,  Mining  Dept.,  Royal  Hungarian  Geol.  Inst.,  April  24, 1908. 

c Squire,  Lovell,  jr.,  Some  observations  on  the  magnesite  of  Silesia:  Trans.  Royal  Geol.  Soc.  of  Corn- 
wall, vol.  9,  pt.  1,  1875,  pp.  59-70. 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


57 


“nests/’  probably  similar  to  what  are  called  “ bowlders”  in  California; 
that  is,  in  large  nodules.  The  deposits  are  covered-  with  soil,  and  the 
peasants  dig  at  random  for  it.  The  analysis  was  given  as  follows : 

Analysis  of  magnesite  from  Frankenstein,  Silesia. 


Silica  (Si02) 5.60 

Alumina  (A1203) ’.85 

Calcium  carbonate  (CaC03) 40 

Magnesium  carbonate  (MgC03) 93.00 


99.85 

As  would  be  expected  from  the  lack  of  iron  or  other  coloring  matter, 
the  magnesite  is  said  to  have  been  very  white.  It  is  not  known 
whether  the  deposits  are  still  worked.  Some  chrysoprase  was  found 
in  veins  close  by. 

GREECE. 

The  principal  magnesite  deposits  of  Greece  are  located  on  the  island 
of  Euboea.®  The  Anglo-Greek  Magnesite  Company,  Limited,  operates 
magnesite  quarries  belonging  to  the  Galataki  monastery,  10  miles  from 
the  port  of  Limni,  whence  the  magnesite  is  shipped.  The  output  of 
this  company  during  1902  and  1903  was  as  follows: 


Magnesite  output  of  Galataki  quarries  and  exports  to  the  United  States,  1902  and  1903. 

[Short  tons.] 


Raw  magnesite. 

Caustic  calcined 
magnesite. 

Dead- 

burned 

magnesite. 

Output. 

Exported 
to  the 
United 
States. 

Output. 

Exported 
to  the 
United 
States. 

1902 

14.600 
26, 300 

6,647 

'3,200 

3.500 

3,550 

578 

1903 

125 

1,200 

The  Society  of  Public  Works  of  Athens  is  exploiting  magnesite  de- 
posits by  underground  workings  at  Mantudi  and  Limni.  During  1902 
it  shipped  to  the  United  States  7,390  metric  tons  of  magnesite  and  92 
tons  of  firebrick;  in  1903,  2,335  tons  of  magnesite;  in  1905,  22,747 
tons  of  magnesite;  and  in  1906,  32,194  tons  of  magnesite,  which  was 
produced  at  Mantudi. b The  total  output  for  Greece  in  1905 c was 
47,849  short  tons,  and  in  1906,  71,015  short  tons,  valued  at  $168,376 
and  $283,333,  respectively.  Magnesite  is  also  found  at  Xirochori,  on 
the  island  of  Euboea;  near  Mariki,  close  to  Thebes  (Bceotia);  and  at 
Hermioni,  in  Argolis. 


a McGinley,  Daniel  E.,  Daily  Consular  Reports,  No.  2276,  Washington,  June  6,  1905,  pp.  3,  4. 
b Bergbau  in  Griechenland:  Zeitschr.  angew.  Chemie,  vol.  21,  January  31, 1908,  p.  225. 
c Quoted  “from  a Government  report”  in  Min.  Jour.  (London),  vol.  82,  1907,  p.  633. 


58 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


Analyses  of  fused  Grecian  magnesite  from  unknown  mines  gave 
Fitzgerald  & Bennie  a the  following  figures: 

Analyses  of  Grecian  magnesite  ( mines  unknown). 


ITALY. 

Magnesite  occurs  at  Casellette,  in  the  Val  di  Susa,  and  at  several 
other  places  in  the  Turin  district,  and  on  the  island  of  Elba.  None 
of  the  deposits  seem  to  be  of  very  large  size.  During  1906  the  Turin 
district  produced  1,463  short  tons  of  raw  magnesite, b valued  at 
$3,958,  and  220  tons  of  calcined  magnesite,0  valued  at  $2,180. 

The  Casellette  deposits d consist  of  great  numbers  of  roughly 
parallel  small  veins  up  to  a few  inches  thick,  in  a serpentinized 
lherzolite.  They  are  close  enough  together  so  that  the  rock  can  be 
broken  down  and  hand  picked. 

No  production  was  reported  from  the  island  of  Elba,  though  the 
deposits  have  been  worked  in  former  years.  The  deposits  are  stock- 
works  of  small  veins0  in  a serpentinized  lherzolite  and  are  appar- 
ently similar  to  those  at  Winchester,  Cal.  (See  p.  38.)  The  fol- 
lowing analyses  of  the  Elba  magnesite  are  given  by  D’Achiardi: 

Analyses  of  magnesite  from  the  island  of  Elba.f 


Water  (H20)  at  110°  C 1. 82  2. 28 

Water  (H20)  above  110°  C 1.  68  2. 08 

Carbon  dioxide  (C02) 44.70  43.86 

Silica  (Si02). 8.15  8.65 

Alumina  (A1203) 1 Trace  .10 

Ferric  oxide  (Fe203) / 

Lime  (CaO) 3.50  .99 

Magnesia  (MgO) 40.84  42.05 


100. 69  100. 01 

MACEDONIA. 

Magnesite  is  found  in  large  quantities  ^ in  Macedonia  near  the 
coast,  not  far  from  the  Greek  border.  Some  of  the  veins  stand  out 

a Physical  properties  of  fused  magnesium  oxide:  Trans.  Am.  Electrochem.  Soc.,  vol.  9,  1906,  p.  102. 
b Rivista  del  Servizio  Minerario,  1906,  Roma,  1907,  p.  xlix. 
cOp.  cit.,  p.  liii. 

d Piolti,  Giuseppe,  Sull’  origine  della  magnesite  di  Casellette  (Val  di  Susa):  Mem.  della  Accad.  scr 
Torino,  2d  ser.,  vol.  47,  pp.  126-142. 

e D’Achiardi,  G.,  La  formazione  della  magnesite  all’  Isolad’  Elba:  Atti  (Mem.)  Soc.toscana  sci.  nat., 
Pisa,  vol.  20,  1904,  pp.  86-134. 

/D’Achiardi,  G.,  op.  cit.,  pp.  123,  129. 

g Der  Bergbau  in  Mazedonien:  Montan  Zeitung  (Graz,  Austria),  vol.  15,  January  1,  1908,  p.  10. 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


59 


like  walls  and  may  be  seen  from  the  sea.  Little  work  has  been  done 
on  them,  but  in  1906  a new  mine  on  the  Chalkidike  Peninsula  began 
operations,  and  a furnace  was  put  up.a 

NORWAY. 

Magnesite  is  being  mined  from  deposits  in  Norway  at  Snarum,* 6 
in  the  Modums  division  of  Buskerud  bailiwick,  on  the  Kroder  line,  a 
spur  of  the  Drammen  Randsfjord  line,  56  kilometers  (35  miles)  from 
Drammen,  the  nearest  city  and  port.  The  magnesite  is  found  in 
serpentinized  olivine  rocks  which  occur  with  schists  and  quartzites. 
Some  of  it  is  crystallized  in  rhombohedra,  but  such  deposits  are 
generally  small.  The  main  deposits  are  ordinarily  granular.  In 
both  forms  the  magnesite  is  nearly  pure  white,  though  the  granular 
magnesite  contains  some  serpentine,  which  occurs  in  more  or  less  dis- 
tinctly marked  bands  or  in  grains  up  to  the  size  of  a bean,  rather 
evenly  distributed  through  the  mass.  The  included  serpentine  is  used 
to  sinter  the  material  in  burning  the  brick. 

There  are  two  principal  fields — the  Dvbingdals,  3 miles  north  of 
Snarum  station,  and  the  Langerud  field,  1J  miles  west  of  Snarum 
station.  In  the  former  the  magnesite  area  covers  about  1,200  square 
meters.  The  veins  average  about  13  feet  in  width,  and  dip  30°  and 
upward.  They  are  worked  by  underhand  stoping.  In  the  Langerud 
field  magnesite  is  exposed  for  135  feet  along  Snarum  or  Hailing  River, 
and  also  100  yards  farther  southwest.  There  are  also  smaller  de- 
posits in  the  neighborhood  of  these  fields.  A factory,  which  has  a 
capacity  of  about  2,500  tons  of  brick  per  year,  is  operated  near 
Snarum. 

The  magnesite  is  sold  calcined  or  as  brick.  An  analysis  of  the  brick 
is  as  follows : 

Analysis  of  magnesite  brick  made  at  Snarum , Norway. 


Silica  (Si02) 9.3 

Manganous  oxide  (MnO) 05 

Aluminum  sulphate  (A1S04) 2. 00 

Iron  oxide  (Fe203) 4.  60 

Phosphoric  anhydride  (P205) 046 

Sulphur  (S) 003 

Lime  (CaO) 00 

Magnesia  (MgO) - 83.  600 

Loss  by  heating .50 


100. 099 

The  magnesite  is  remarkable  in  that  it  shows  no  lime.  According 
to  tests  quoted  in  the  article  referred  to,  brick  from  the  Snarum 
factory  are  more  heat  resistant  than  the  Austrian  Veitsch  brick. 

“The  mineral  wealth  of  Macedonia:  Mining  Jour.  (London),  vol.  83,  1908,  p.  251. 

6 Daumann,  E.,  Magnesitfran  Snarum:  Bihang  till  Jern-Kontorets  Annaler  for  1905,  Stockholm,  1905, 
pp.  222-235. 


60 


MAGNESITE  DEPOSITS  OF  CALIFORNIA. 


During  1907  a the  output  of  the  works  was  900  tons  of  calcined 
magnesite,  valued  at  $12,060,  and  125  tons  of  brick,  valued  at  $3,685- 

RUSSIA. 

Magnesite  occurs  in  Russia  in  the  Uphim  Mountain  district  of  the 
Urals,  and  during  1906  one  firm,  the  Magnesite  Company,  produced 
26,320  tons  of  magnesite. b 

AFRICA. 

TRANSVAAL. 

Extensive  deposits  of  magnesite  occur  between  Kaapmuiden  and 
Malelane,  2 miles  south  of  the  Pretoria-Delagoa  Bay  Railway,  87 
miles  from  Louren^o  Marquez  and  300  miles  from  Johannesburg. 
The  magnesite  is  found  in  a great  number  of  veins,  ranging  up  to  4 
feet  in  thickness,  and  has  been  exploited  to  a depth  of  95  feet.c  Most 
of  the  veins  are  much  thinner  than  the  limit  of  width  given,  but 
there  seems  to  be  a large  area  of  serpentine  carrying  thejn.  The 
serpentine  is  here  3 miles  wide.  Some  of  the  magnesite  is  soft  and 
powdery,  like  that  at  Red  Mountain,  Santa  Clara  County,  Cal.  (p.  35). 

One  4 to  6 inch  veind  is  described  as  “ entirely  of  pure,  glassy- 
looking magnesite.”  Hall  gives  the  following  analysis  of  a picked 
specimen  from  these  deposits: 

Analysis  of  magnesite  from  Malelane,  Transvaal. 


Magnesia  (MgO) 45.272 

Carbon  dioxide  (C02) 49.  80 

Silica  (Si02) 2.30 

Lime  (CaO) 

Ferric  oxide  (Fe203) 80 

Moisture  at  110°  C.. 16 


98. 332 

Quartz  forming  thin  coatings  on  the  magnesite  is  found  at  various 
places. 

The  rock  is  used  for  making  carbon  dioxide,  and  much  of  it  is 
calcined  by  producer  gas  at  about  1,100°  C.  and  mixed,  either  in 
lump  or  ground,  with  magnesium  chloride  imported  from  Germany 
to  make  oxychloride  cement.  Most  of  the  output  goes  into  this 
product,  for  which  its  freedom  from  lime  makes  the  material  par- 
ticularly well  suited. 

a Letter  from  Dr.  Johan  H.  L.  Vogt,  professor  of  metallurgy  at  the  University  of  Kristiania,  Feb- 
ruary 15,  1908. 

b Magnesite  and  chrome  iron  ore  in  the  Urals:  Mining  Jour.  (London),  vol.  82,  December  14,  1907, 
paragraph  on  p.  721. 

cllall,  A.  L.,  The  magnesite  deposits  of  Malelane:  Rept.  Geol.  Survey,  Transvaal  Mines  Dept.,  for 
190(3,  Pretoria,  1907,  pp.  127-132. 

d Hall,  A.  L.,  op.  cit.,pp.  128-129.  For  further  reference  to  the  Malelane  deposits  see  Hollis,  W.  S., 
Magnesite  deposits  in  South  Africa:  Daily  Consular  Repts.,  No.  2276,  Washington,  June  6,  1905,  pp. 
7-8;  Praagh,  L.  V.,  The  Transvaal  and  its  mines,  London  and  Johannesburg,  1906,  pp.  633-634. 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


61 


OTHER  AFRICAN  DEPOSITS. 

Henry  W.  Nevinson  ° speaks  of  “the  volcanic  district  of  North 
Bihe,  with  its  boiling  springs  and  great  deposits  of  magnesia.”  The 
Bihe  region  is  a couple  of  hundred  miles  east  of  Benguela,  in  Portu- 
guese West  Africa.  No  further  details  are  given,  but  the  association 
with  boiling  springs  suggests  that  such  a magnesian  deposit  would 
probably  be  hydromagnesite,  similar  to  the  deposits  in  British 
Columbia.  (See  p.  53.) 

“Magnesia,”  6 by  which  magnesite  is  probably  meant,  is  reported 
to  occur  in  Mashonaland,  near  the  western  side  of  Africa,  notably 
at  Umtali  and  at  the  great  Zimbabwe  ruins — at  the  latter  place  in 
steatite. 


ASIA. 

INDIA. 

Madras. — Magnesite  is  found  at  a number  of  places  in  India,  the 
most  important  of  which  seems  to  be  in  the  Chalk  Hills,  4 miles 
northwest  of  Salem,  Madras  Presidency,  in  the  southern  part  of  the 
Indian  Peninsula.  The  magnesite  here  occurs  in  interlacing  veins, 
some  of  which  stand  several  feet  above  the  surrounding  talcose, 
serpentinized,  and  other  magnesian  rocks.  From  the  whiteness  of 
the  outcropping  magnesite  the  name  “Chalk  Hills”  has  been  given 
to  the  range.  The  main  magnesite  deposits  occur  over  an  area  of  10 
square  miles, c and  there  are  various  outlying  deposits.  During  1905 
the  production  was  2,035  tons  of  magnesite,  valued  at  $2,750,  and 
during  1906  1,832  tons,  valued  at  $2,440/ 

Mysore. — Magnesite  deposits  occur  at  a number  of  points  near 
Mavinhalli  and  Kadakola,  in  Mysore/  in  the  south-central  part  of 
the  Indian  Peninsula.  The  deposits  do  not  seem  to  be  of  commer- 
cial importance  at  present,  though  the  magnesite  has  been  used 
locally  as  a substitute  for  lime/  There  are  also  reported  to  be 
many  deposits  of  magnesite  in  the  neighborhood  of  Yelwal/  but 
their  extent  is  unknown. 

Ceylon. — “Hydromagnesite  does  not  occur  in  commercial  quanti- 
ties so  far  as  known,  but  has  some  local  use.”  h 

a The  slave  trade  in  Africa:  Harper’s  Magazine,  vol.  112,  December,  1905,  p.  116. 

&Swan,  Robert  M.  W.,  Notes  on  the  geography  and  meteorology  of  Mashonaland,  in  Bent,  J.  T. 
Rained  cities  of  Mashonaland,  London,  1892,  p.  347. 

c King,  W.,  jr.,  and  Foote,  R.  B.,  On  the  geological  structure  of  the  districts  of  Triehinopoly,  Salem, 
and  South  Arcot  included  on  sheet  79  of  the  Indian  atlas:  Mem.  Geol.  Survey  India,  1865,  pp.  312-327. 

d Dennison,  E.  Haldeman,  Daily  Consular  Repts.,  No.  3138,  Washington,  March  31,  1908,  pp.  1-2. 

« Primrose,  A.,  Notes  on  magnesite  in  the  Mysore  district:  Rec.  Mysore  Geol.  Dept.,  vol.  4 (1904?). 
pp.  147-157. 

/Op  cit.,  p.  151. 

9 Ram,  B.  Jaya,  Summary  of  the  work  done  during  the  year  1904-5:  Rec.  Mysore  Geol.  Dept.,  vol. 
6 (1906?),  p.  52. 

ft  Parsons,  James,  principal  mineral  surveyor  for  Ceylon,  letter,  March  5, 1908. 


62 


MAGNESITE  DEPOSITS  OE  CALIFORNIA. 


AUSTRALIA. 


QUEENSLAND. 

In  Queensland  a magnesite  occurs  in  the  Normanton  district  in  the 
Gulf  country;  in  the  Rockhampton  district  on  Dinner,  Sawpit  and 
Stewarts  creeks;  at  Stanwell,  Islapot,  Moonmera,  and  the  Pointer, 
near  Yamba.  In  other  districts  it  occurs  at  Clermont,  Toorwomba, 
Ipswich,  Kilkivan,  and  Newellton.  The  deposit  at  Kilkivan  is 
thought  to  be  the  largest,  though  all  the  deposits  are  so  small  that  it 
is  improbable  that  any  of  them  can  be  worked  commercially. 

NEW  SOUTH  WALES. 


Small  deposits  are  known  in  New  South  Wales  6 in  the  diamond 
fields  at  Bingera,  county  of  Murchison,  and  near  Mudgee.  At  Two- 
mile  Flats,  near  Mudgee,  pebbles  in  waste  heaps  were  cemented 
together  by  it.  On  Cudgebegong  Creek  it  forms  in  peculiar  vermicu- 
lar or  wormlike  forms.  Other  localities  in  New  South  Wales  are 
Lochlan  River,  Mooly  Gully,  and  Scone,  county  of  Brisbane;  Louisa 
and  Lewis  Pond  creeks,  county  of  Wellington;  and  Barraba,  county 
of  Darling.  None  of  these  deposits  are  of  commercial  value,  but 
recently  magnesite  has  been  discovered  in  what  appears  to  be  con- 
siderable quantity  c 3J  miles  northwest  of  Fifield.  Over  an  area  of 
100  acres  it  crops  out  through  red  clay  as  large  rounded  blocks  of 
pure -white  material.  It  is  said  to  be  capable  of  yielding  many 
thousand  tons  of  magnesite  at  a cost  not  exceeding  38  cents  per  ton, 
on  drays.  A partial  analysis  of  this  magnesite  is  as  follows: 

Partial  analysis  of  magnesite  from  Fifield,  New  South  Wales. 


Magnesium  carbonate  (MgC03) 99.01 

Lime  (CaO) Absent. 

Ferric  oxide  (Fe203),l  ^ 

Alumina  ( A1203) / 

Gangue  (sand) •. 42 


SOUTH  AUSTRALIA. 


99.97 


Large  deposits  are  reported  in  South  Australia,  but  so  far  no  work 
has  been  done  on  them. 


TASMANIA. 


In  Tasmania  magnesite  “occurs  in  serpentine,  Parson’s  Hood 
Mountain;  in  veins,  Trial  Harbor;  Meredith  Range;  Dundas; 
Hazlewood.  ”d 


a Dunstan,  B.,  Magnesite  in  Queensland,  quoted  in  Queensland  Gov.  Min.  Jour.  (Brisbane),  vol.  8, 
August,  1907,  p.  405. 

b Liversidge,  Archibald,  The  minerals  of  New  South  Wales,  2d  ed.,  Sydney,  1882,  p.  176. 
c Jaquet,  J.  B.,  Magnesite  at  Fifield:  Australian  Min.  Standard,  vol.  38, 1907,  p.  172. 
d Petterd,  W.  F.,  Minerals  of  Tasmania:  Papers  and  Proc.  Royal  Soc.  Tasmania,  1893,  Hobart, 
1894,  p.  45. 


MAGNESITE  DEPOSITS  IN  OTHER  COUNTRIES. 


63 


OCEANICA. 

NEW  CALEDONIA. 

Extensive  deposits  of  magnesite  occur  on  the  north  end  of  the 
west  coast  of  New  Caledonia,®  at  the  contact  of  black  schists  with 
serpentine,  particularly  between  Koumac  and  Voh.  A specimen 
obtained  near  Koumac  gave  the  following  analysis: 

Analysis  of  magnesite  from  vicinity  of  Koumac , New  Caledonia. 


Silica  and  insoluble  (Si02,  etc.) 0. 8 

Ferric  oxide  (Fe203) 8 

Lime  (CaO) 3.3 

Magnesia  (MgO) 42.4 

Carbonic  anhydride  (C02) 51.5 

Moisture 4 


99.2 

It  will  at  once  be  noticed  that  the  lime  content  is  too  great  to  per- 
mit the  use  of  the  material  in  oxychloride  cement.  The  freight  is 
high  from  New  Caledonia  to  Europe  or  America,  so  that  the  only 
exports  have  been  a trial  shipment  of  42  tons  in  1907. 6 

a Glasser,  Ed.  M.,  Report  a M.  le  ministre  des  colonies  sur  les  richesses  minerales  de  la  Nouvelle- 
Caledonie:  Ann.  des  mines,  10th  ser.,  vol.  5,  pt.  5,  1904,  pp.  548-549. 

b Eng.  and  Min.  Jour.,  vol.  85,  February  1, 1908,  p.  283,  quoting  from  Bulletin  du  Commerce,  Noumea, 
New  Caledonia. 


INDEX. 


A.  Page. 

Africa,  magnesite  deposits  of 60-61 

Alameda  claim,  description  of 33-37 

magnesite  of,  analysis  of 36 

Alameda  County , magnesite  deposits  on 37 

Alba  levis,  manufacture  and  use  of 13 

American  Magnesite  Co.,  deposits  of 33-34 

American  River,  magnesite  deposits  in 52 

Arizona,  magnesite  in 7 

Arnold,  E.  W.,  on  Red  Slide  magnesite  de- 
posits  26,27 

Ashcroft,  B.  C.,  magnesite  deposits  near 54 

Asia,  magnesite  deposits  of 61 

Atlin,  B.  C.,  magnesite  deposits  at 53-54 

magnesite  at,  analysis  of 53 

Auckland,  magnesite  deposits  near 49 

Australia,  magnesite  deposits  of 62 

Austria,  magnesite  deposits  in 55 

B. 

Bakersfield,  magnesite  deposits  near 39 

Banta’s  camp  deposit,  description  of 37 

Bartlett,  W.  P.,  on  American  River  deposits.  52 

Bartlett  & Stanley,  magnesite  deposit  of 29-31 

magnesite  of,  analysis  of 30 

Bay  Cities  Water  Co.,  deposits  of 32-33 

deposits  of,  structure  of,  plate  showing.  32 
Benguela,  West  Africa,  magnesite  deposits 

near 61 

Blanco  claim,  description  of 29-31 

Brick,  magnesia,  manufacture  of 11,12 

British  Columbia,  magnesite  deposits  in 53-54 

Brucite,  precipitation  by 20 

C. 

Calcination,  temperature  of 9-10 

California,  magnesite  deposits  in 7-8 

magnesite  deposits  in,  detailed  descrip- 
tions of 17-52 

location  of,  map  showing 7 

production  of 16 

technology  of 8-15 

See  also  Magnesite. 

wages  in 15 

Cambria,  magnesite  deposits  near 38 

Canada,  magnesite  deposits  in 53-54 

Canada  claim,  description  of 36 

Carbon  dioxide,  manufacture  and  use  of 8-9 

Cazadero,  magnesite  deposit  near,  view  of 20 

Cement.  See  Oxychloride  cement. 

Ceylon,  magnesite  deposits  of 61 

Chiles  Valley,  magnesite  deposits  in 29, 31 

51136— Bull.  355—08 5 


Page. 

Clay,  magnesite  weathered  beneath,  plate 


showing 20 

Cloverdale,  magnesite  deposits  near 21, 22, 24 

Coast  Range,  magnesite  deposits  in 21-39 

Cochrane,  Mrs.  A.  F.  magnesite  deposit  of. . . 33 

magnesite  of,  analysis  of 33 

Conchoidal  fracture,  specimens  showing, 

plate  showing 8 

Coyote,  magnesite  deposit  near 31-32,37 

magnesite  near,  analysis  of 32 

Creon  deposit,  analysis  of 23 

description  of 22-23 

Crucibles,  magnesia,  manufacture  of 11-12 

Cummings,  Pat,  magnesite  claim  of 24 

D. 

Damascus  deposits,  magnesite  of ’. 52' 

I Deer  Creek  deposits,  analysis  of 40 

J description  of 39-40 

plate  showing 38 

Dike  cutting  magnesite,  plate  showing 40 

E. 

East  Austin  Creek,  magnesite  deposits  near.  26 

Eckert  ranch  deposit,  analysis  of 23,24 

description  of 23-24 

Elba,  magnesite  deposits  of 58 

magnesite  of,  analysis  of 58 

Electric  furnace,  use  of 13 

Epsom  salts,  manufacture  of 7, 13 

I Europe,  magnesite  deposits  in 55-60 

Exeter,  magnesite  deposits  near 49 

F. 

Field  work,  period  of 8 

Fitzgerald,  A.  J.,  on  magnesia  manufacture. . 12 

Fitzgerald  and  Bennie,  experiments  by 14 

Foreign  countries,  magnesite  deposits  in. . 7-8, 52-63 

Fresno  County,  magnesite  deposits  in 50-51 

Fusing  point,  determination  of 14-15 

G. 

Germany,  magnesite  deposits  of 56-57 

magnesite  of,  analysis  of 57 

Gilliam  Creek,  magnesite  deposits  on 24-25 

magnesite  from,  analysis  of 25 

magnesite  from,  cost  of 15 

Goodwin  and  Mailey,  experiments  of 14 

Governor  claim,  magnesite  of 51 

Greasy  Camp  Creek,  magnesite  deposit  on 31 

Greece,  magnesite  deposits  of 57-58 

magnesite  of,  analysis  of 58 

shipments  of,  to  California 16 


65 


66 


INDEX. 


H. 

Hall  (George)  ranch  deposit,  description  of. . . 

Hixon  ranch  deposit,  analysis  of 

description  of 

specimen  of,  view  of 

view  of 

Hungary,  magnesite  deposits  of 

magnesite  of,  analyses  of 

wages  in 

I. 

Incandescent  lamps,  use  of  magnesia  in 

India,  magnesite  deposits  of 

Italy,  magnesite  deposits  of 

magnesite  of,  analysis  of 

K. 

Kern  County,  magnesite  deposits  in 

King  claim,  description  of 

Kings  River,  magnesite  deposits  on 

magnesite  on,  analysis  of 

cost  of 

views  of 

Kiser  deposit,  description  of 

Koebig,  Julius,  on  Lower  California,  magne- 
site  

L. 

Lamps.  See  Incandescent  lamps. 

Lemora  Cove,  magnesite  deposits  near 

Literature,  scantiness  of 

Livermore,  magnesite  deposits  near 

Lower  California,  Mexico,  magnesite  deposits 

in 

magnesite  in,  analyses  of 

M. 

Macedonia,  magnesite  deposits  of 

Madeira  deposit,  description  of 

Madras,  magnesite  deposits  of 

Magnesia  brick,  shapes,  and  crucibles,  bind- 
ers for 

manufacture  of.  

Magnesite,  bowlders  of 

bowlders  of,  view  of 

calcination  of 

character  of 

cracks  in,  plate  showing 

deposits  of,  in  California,  description  of. . . 
in  foreign  countries,  descriptions  of . . . 

dike  cutting,  view  of 

distribution  of 

map  showing 

formation  of 

fusing  point  of 

importation  of 

fracture  of,  plate  showing 

manufacture  of 

market  for 

precipitation  of 

production  of 

properties  of 

sintering  of 

structure  of,  plate  showing 

uses  of 


Page. 

Magnesite,  veins  of,  plates  showing ...  20, 42, 44, 50 

prominence  of 18-19 

weathering  of 19;  34-35 

plates  showing 18,20 

Magnesite  Products  Company,  magnesite  de- 
posits of 22 

Magnesium,  source  of 15 

Magnesium  carbonates,  uses  of ' 13 

Mammoth  vein,  description  of 34 

Map  of  California,  showing  magnesite  deposits  7 

Mariposa  County,  magnesite  deposits  of 51752 

Markets,  data  on 15-16 

Maryland,  magnesite  in 7 

Massachusetts,  magnesite  in 7 

Matthai,  Frank,  magnesite  deposit  of 31 

Mendocino  County,  magnesite  deposits  in 21-22 

Mexico,  magnesite  deposits  in 54-55 

Morgan  Hill,  magnesite  deposit  near 33 

Mysore,  magnesite  deposits  of 61 

N. 

Napa  County,  description  of 28 

magnesite  deposits  in 28-31 

magnesite  of,  cost  of 16 

Naranjo,  magnesite  deposits  near 49 

Nevada,  magnesite  in 7 

New  Almaden,  magnesite  deposits  near 37 

New  Caledonia,  magnesite  deposits  of 63 

magnesite  of,  analysis  of 63 

New  South  Wales,  magnesite  deposits  of 62 

magnesite  of,  analysis  of 62 

New  York  City,  magnesite  in,  price  of 16 

North  America,  magnesite  deposits  in 53-55 

See  also  California. 

Norton  (Ed.)  ranch,  magnesite  deposits  on. . 28 

Norway,  magnesite  deposits  in 59-60 

magnesite  of,  analysis  of 59 

O. 

Oakland,  carbon  dioxide  made  at. . : 8 

magnesia  brick  plant  at 11 

Oceania,  magnesite  deposits  of 63 

magnesite  of,  analysis  of 63 


Oxychloride  cement,  manufacture  and  uses  of  13-14 
P. 


Pennsylvania,  magnesite  in • 7 

Placer  County,  magnesite  deposits  of 52 

Pope  Valley,  magnesite  deposit  in 28 

magnesite  deposit  in,  view  of 20 

Porterville,  magnesite  deposits  near 39-46 

magnesite  deposits  near,  map  of 42 

section  of,  figure  showing 43 

views  of 40,42,44 

magnesite  from,  analyses  of 4 

cost  of 15 

specimens  of,  plate  showing 22 

Power,  H.  T.,  on  Damascus  deposits 52 

Priest,  D.  C.,  magnesite  deposit  of 31 

' Q- 

Quebec,  magnesite  deposits  in 53 

magnesite  of,  analysis  of 53 

Queensland,  magnesite  deposits  of 62 


Page. 

24 

21 

21-22 

22 

20 

15,56 

-56 

15 

15 

61 

58 

58 

39 

37 

50-51 

50 

■ 16 

50 

38 

54 

49 

8 

33 

54-55 

55 

58-59 

25 

61 

12 

11-13 

20 

20 

9-10 

8 

22 

17-52 

52-63 

40 

7-8 

7 

17-18 

14-15 

16-17 

8 

8-15 

15-16 ‘ 

20 

16 

8 

12-13 

32 

8-15 


INDEX. 


67 


R.  Page. 

Red  Mountain,  magnesite  deposits  at 33-37 

magnesite  at,  analysis  of 36 

Red  Slide  deposit,  analysis  of ' 27 

description  of 26-27 

Riverside  County,  magnesite  deposits  in 38-39 

Round  Valley,  magnesite  deposits  in 48-49 

Russell,  E.  T.,  magnesite  deposit  of 31 

Russia,  magnesite  deposits  of 60 

Rutherford,  magnesite  deposits  near 31 

S. 

San  Benito  County,  magnesite  deposits  in . . . 38 

San  Felipe  Creek,  magnesite  deposit  on 32 

Sanger,  magnesite  deposits  near 50 

magnesite  deposits  near,  view  of . . 50 

San  Jose,  magnesite  deposits  near 37 

San  Luis  Obispo  County,  magnesite  deposits 

in 38 

Santa  Barbara  County,  magnesite  deposits 

in 38 

Santa  Clara  County,  magnesite  deposits  in  . . 31-37 
Santa  Margarita,  Mexico,  magnesite  deposits 

of 54-55 

magnesite  of,  analyses  of 55 

Serpentine,  decomposition  of 18,19-20 

description  of 17 

magnesite  in 17 

plates  showing 20,38 

occurrence  of 17 

Shrinkage,  cracks  in  magnesite  due  to,  view  of  22 

Sierra  Nevada,  magnesite  deposits  in 39-52 

Snow  Cap  claim,  magnesite  deposit  of 50-51 

magnesite  deposit  of,  view  of 50 

magnesite  of,  analysis  of 50 

Snowflake  claim,  description  of 29-31 

Soda  Creek  Canyon,  magnesite  deposit  in 31 

Sonoma  County,  magnesite  deposits  in 22-28 

magnesite  of,  analyses  of 23, 24, 25, 27 

cost  of 16 

Sonoma  Magnesite  Co.,  magnesite  deposits  of.  26 

magnesite  deposits  of,  view  of 20 

South  Africa,  cement  making  in 13 

magnesite  deposits  of 60 

magnesite  of,  analysis  of 60 

South  America,  magnesite  deposits  of 55 

South  Australia,  magnesite  deposits  of 62 

Spinks,  C.  H.,  on  Red  Mountain  deposits 35 


Page. 


Stanislaus  County,  magnesite  deposits  in 34,37 

Success  schoolhouse,  magnesite  deposits  near.  46-48 
magnesite  near,  analysis  of 47 

T. 

Tailholt,  magnesite  deposits  near 39 

Tasmania,  magnesite  deposits  of 62 

Transvaal,  magnesite  deposits  of 60 

magnesite  of,  analysis  oT 60 

Tubing,  magnesite,  uses  for 14 

Tulare  County,  magnesite  deposits  in...  -. 3y-49 

Tule  River  (South  Fork),  magnesite  deposits 

on 46-48 

magnesite  on,  analysis  of 47 

Tuolumne  County,  magnesite  deposits  of 51-52 

Turner,  H.  W.,  on  Damascus  deposits 52 

V. 

Van  Hise,  C.  R.,  on  derivation  of  magnesite. . 18 

Veins,  magnesite,  depth  of 18-19 

description  of 20 

prominence  of 18-19 

Venezuela,  magnesite  deposits  of 55 

W. 

Walkers  Pass,  magnesite  deposits  in 39 

Walters  deposit,  description  of 28-29 

view  of 20 

Ward,  G.  D.,  magnesite  deposit  of 50 

Watts,  O.  P.,  on  magnesia  crucibles 11-12 

Weathering,  effect  of,  plate  showing 18 

West  Africa,  magnesite  deposits  of 61 

Western  Carbonic  Acid  Gas  Co.,  magnesite 

deposit  of 25 

plant  of 8 

diagram  of 9 

White  River  deposits,  description  of 39 

White  Rock  deposit,  description  of 28-29 

Willamette  Pulp  and  Paper  Co.,  magnesite 

deposit  of 41 

magnesite  deposit  of,  views  of '2, 44 

plant  of,  figure  showing 45 

view  of 44 

Winchester,  magnesite  deposits  near 38-39 

magnesite  near,  analysis  of 39 

view  of 38 

Y. 

Yokohl  Valley,  magnesite  deposits  in 49 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  DIRECTOR 


Bulletin  356 


GEOLOGY 

OF  THE 

GREAT  FALLS  COAL  FIELD 


MONTANA 


BY 

CASSIUS  A.  FISHER 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1909 


CONTENTS. 


Page. 

Introduction 7 

Literature 7 

Topography 14 

Relief 14 

Drainage 16 

Missouri  River 16 

Sun  River 17 

Smith  River 17 

Belt  Creek 18 

Other  small  streams 19 

Culture 20 

Descriptive  geology 21 

Stratigraphy 21 

General  outline 21 

Sedimentary  rocks 24 

Carboniferous  system 24 

Madison  limestone 24 

General  statement 24 

Castle  limestone 24 

Quadrant  formation 25 

Character  and  extent 25 

Age 27 

Jurassic  system 27 

Ellis  formation 27 

Character  and  extent 27 

Fossils 28 

Morrison  shale  (?) 28 

Character  and  extent 28 

Fossils 30 

Cretaceous  system 30 

Kootenai  formation 30 

General  statement 30 

Character  and  extent 31 

Fossils 33 

Colorado  shale 36 

General  statement 36 

Character  and  extent 36 

Fossils 38 

Tertiary  and  quaternary  systems 39 

Terrace  gravel 39 

General  statement 39 

Character 39 

Mode  of  occurrence 39 

Origin  of  terraces 40 

Age 40 


3 


4 


CONTENTS. 


Descriptive  geology — Continued. 

Stratigraphy — Continued. 

Sedimentary  rocks — Continued.  • 

Tertiary  and  quaternary  system — Continued.  Page. 

Glacial  deposits 41 

General  statement 41 

Drift 41 

Lake  sediments 42 

Alluvium 43 

General  statement 43 

Character  and  extent 43 

Dune  sand 43 

Character  and  extent 43 

Source 44 

Igneous  rocks 44 

Metamorphic  rocks 46 

Structure 47 

Plains  province 47 

General  conditions 47  ' 

Domes 48 

Faults 49 

Little  Belt  Mountains 49 

High  wood  Mountains 50 

Economic  geology 50 

General  statement 50 

Coal 50 

Geological  occurrence 50 

Sand  Coulee  area 51 

Location  and  extent 51 

Character  and  thickness  of  coal  bed 52 

Development 53 

Belt  Creek  mines 54 

General  statement 54 

Mines  operated 54 

Anaconda  Copper  Mining  Company  mine 54 

Schmauch  mine 57 

Millard  mine 57 

Richardson  mine 57 

Orr  mine 57 

Abandoned  mines 58 

Hill  mine 58 

Buzzo  or  Hill  mine 58 

Boston  and  Montana  mine 58 

Herman  & Powell  mine 59 

Watson  mine 59 

Brady  mine 59 

American  Smelting  and  Refining  Company's  mine 59 

Prospects 60 

Entry  prospects 60 

Diamond-drill  prospects 60 

Sand  Coulee  mines 60 

General  statement 60 

Mines  operated 61 

Cottonwood  Coal  Company  mine 61 


CONTENTS. 


5 


Economic  geology — Continued. 

Coal — Continued. 

Sand  Coulee  area — Continued. 

Sand  Coulee  mines — Continued. 

Mines  operated — Continued.  Pase- 

Nelson  mines 63 

Gerber  mine 64 

Mount  Oregon  Coal  Company  mine 64 

Dahn  mine 65 

Brown  mine 65 

Stainsby  mine 65 

Abandoned  mines 66 

Smith  River  mines 66 

General  statement 66 

Mines  operated 66 

Carville  mine 66 

Gibson  mine 67 

Patterson  and  Rice  mines 67 

Bickett  mine 67 

Love  mine 67 

Prospects 68 

Otter  Creek  area 68 

Location  and  extent 68 

Character  and  thickness  of  coal  bed 69 

Development 69 

General  statement 69 

Mines  operated 70 

Nollar  mine 70 

Chamber  Brothers’  mine 70 

Nullinger  mine 70 

Abandoned  mines 71 

Sage  Creek  area 71 

Location  and  extent 71 

Character  and  thickness  of  coal  bed 72 

Development 73 

General  statement 73 

Mines  operated 73 

Schultz  mine 73 

Seman  mine 74 

Hughes  mine 74 

Abandoned  mines 75 

Corwin  & McGregor  mine 75 

Fisher  mine 75 

West  Fork  of  Willow  Creek  mine 75 

Sage  Creek  Sheep  Company  mine 75 

Prospects 76 

Entry  prospects 76 

Diamond-drill  prospects 77 

Character  of  coal 77 

General  statement 77 

Physical  properties 77 

Chemical  properties ; 79 

Future  development 81 

Timber 82 

Index 83 


ILLUSTRATIONS. 


Page. 


Plate  I.  Geologic  map  of  the  Great  Falls  region,  Montana In  pocket. 

II.  Map  of  the  Great  Falls  region,  Montana,  showing  coal  lands 7 

III.  Dry  bed  of  Belt  Creek  near  Belt,  Montana 18 

IV.  Columnar  sections  showing  stratigraphy  along  Belt  Creek  -valley, 

Montana 20 

V.  Madison  limestone  overlain  by  shale  of  the  Quadrant  formation, 

near  Riceville,  Montana 24 

VI.  Basal  Jurassic  sandstone  lying  unconformably  on  Madison  limestone, 

near  Stockett,  Montana 28 

VII.  Columnar  sections  showing  stratigraphy  in  different  parts  of  Great 

Falls  region,  Montana 30 

VIII.  Sections  of  coal  in  Belt  Creek  and  Smith  River  districts,  Montana. . 54 

IX.  Anaconda  Copper  Mining  Company’s  coal  plant  at  Belt,  Montana. . . 56 

X.  Sections  of  coal  bed  in  Sand  Coulee  district,  Montana 60 

XI.  A,  Cottonwood  Coal  Company’s  mine  No.  5,  near  Stockett,  Montana; 

B,  Nelson  coal  mine  and  plant  at  Sand  Coulee,  Montana 62 

XII.  Sections  of  coal  bed  in  Otter  Creek  and  Sage  Creek  areas,  Montana..  70 
Fig.  1.  Ideal  cross  section,  showing  relations  between  the  two  lake  deposits 

in  Missouri  River  valley  west  of  Great  Falls 42 

2.  Ideal  longitudinal  section,  showing  the  relation  of  the  two  lake  de- 
posits shown  in  fig.  1 to  the  drift  dam  and  the  ice  dam 43 


6 


'Ll'C’.'J 


BULLETIN  NO.  356  Pl_ 


MAP  OF  THE  GREAT  FALLS  REGION,  MONTANA,  SHOWING  COAL  LANDS. 


nr 


PL.  II 


MAP 


. 17  N. 


GEOLOGY  OF  THE  GREAT  FALLS  COAL  FIELD, 

MONTANA. 


By  Cassius  A.  Fisher. 


INTRODUCTION. 

This  report  is  the  result  of  field  studies  made  during  the  season  of 
1906.  It  is  designed  mainly  to  furnish  information  regarding  the 
character  and  extent  of  £he  coal  resources  of  the  Great  Falls  region. 
It  includes  a description  of  the  rock  formations,  indicating  their 
character,  distribution,  structure,  and  stratigraphic  relations,  and  also 
a brief  statement  of  mineral  resources  other  than  coal. 

The  region  under  consideration  comprises  1,500  square  miles, 
situated  mainly  in  north-central  Montana,  and  extending  along  the 
base  of  the  Rocky  Mountain  front  range  from  a point  10  miles  west  of 
Judith  River  to  a short  distance  beyond  the  Missouri.  The  location 
and  orographic  relations  of  the  field  are  shown  in  the  index  map  on 
PI.  I (in  pocket).  The  field  lies  principally  in  Cascade  County,  but 
includes  portions  of  Fergus  and  Chouteau  counties,  having  as  its 
boundary  on  the  south  the  Big  and  Little  Belt  mountains  and  on  the 
north  the  Great  Plains  and  the  High  wood  Mountains. 

Throughout  the  work  the  author  was  assisted  by  II.  M.  Eakin,  who 
mapped  portions  of  the  area,  measured  many  sections,  and  assisted  in 
compiling  the  results  for  publication.  Assistance  in  the  field  was  also 
rendered  by  W.  R.  Calvert,  J.  D.  Pollock,  A.  J.  Hazlewood,  and  D.  E. 
Winchester,  and  the  author  is  indebted  to  S.  B.  Robbins,  project 
engineer  of  the  Sun  River  reclamation  project,  and  to  O.  C.  Mortson, 
formerly  county  surveyor  of  Cascade  County,  for  valuable  information 
placed  at  his  disposal  in  connection  with  the  preparation  of  the  work. 

LITERATURE. 

The  western  half  of  the  area  here  described  as  the  Great  Falls 
coal  field  has  never  been  systematically  studied  by  previous  workers  in 
geology,  but  several  reports  dealing  with  the  general  geology  of  dif- 
ferent parts  of  the  district  to  the  east  in  the  vicinity  of  the  Highwood 
and  Little  Belt  Mountains  have  been  published. 


7 


8 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


The  Great  Falls  of  Missouri  River,  also  the  Giant  Springs,  are 
phenomena  which  have  attracted  widespread  attention  since  the 
earliest  explorers  followed  up  the  course  of  the  Missouri  to  the  north- 
west, and  a number  of  descriptions  of  them  have  been  published. 
Those  appearing  first  set  forth  mainly  the  size  and  beauty  of  these 
falls,  but  later,  as  the  region  was  settled  and  the  town  of  Great  Falls 
promised  to  become  an  important  industrial  center,  a number  of 
articles  dealing  with  their  utility  were  published  in  technical  journals. 
Captain  Lewis,  of  the  Lewis  and  Clark  expedition,  which  was  made 
in  1804-1806,  was  the  first  to  give  an  accurate  account  of  the  Great 
Falls  and  Giant  Springs,  and  to  describe  certain  features  of  the  geog- 
raphy of  the  region  bordering  this  portion  of  Missouri  River.  It  is 
probable  that  other  early  explorers  were  attracted  by  the  Great  Falls 
and  mentioned  their  occurrence  and  surroundings  in  describing  the 
Northwest  Territory. 

The  coals  have  been  the  subject  of  much  of  the  geologic  literature 
concerning  this  region,  and  many,  if  not  most,  of  the  more  important 
geologic  discoveries  have  been  made  in  connection  with  a study  of 
the  nature  and  extent  of  these  deposits.  The  investigations  of  the 
geologists  of  the  Hayden  and  Transcontinental  surveys  in  this  part  of 
the  United  States  were  confined  mainly  to  the  region  lying  east  of 
Great  Falls,  and  did  not  extend  into  the  western  part  of  the  field.  In 
1880  W.  M.  Davis  published  an  article  a in  which  he  gave  an  account  of 
the  geology  of  the  Little  Belt  and  Highwood  mountains  and  the  ad- 
joining plains.  During  the  same  year  George  H.  Eldridge  described 
the  geology  of  the  Great  Falls  coal  field.  The  next  observer  in  the 
field  was  J.  S.  Newberry,  who,  in  connection  with  an  investigation  of 
the  surface  geology  of  the  country  bordering  the  Northern  Pacific 
Railroad,  including  the  Great  Falls  coal  field,  discovered  fossil  plants 
associated  with  the  coals,  which  established  the  Kootenai  age  of  these 
deposits.  After  this  discovery  articles  were  published  by  Newberry 
and  Fontaine  dealing  especially  with  the  age  of  these  coal-bearing 
rocks,  as  determined  from  their  fossil  floras,  and  their  correlation 
with  Kootenai  rocks  of  other  localities  in  the  United  States  and 
Canada.  In  the  spring  of  1891  W.  II.  Weed,  of  the  United  States 
Geological  Survey,  while  making  a general  study'  of  the  coal  fields  of 
Montana,  visited  this  region  and  later  described  the  coal  deposits  in 
considerable  detail.  The  Geological  Survey  has  published  an  annual 
account  of  coal  operations  in  this  field  since  1888,  and  also  a number 
of  general  reports  on  the  coals  of  Montana  and  the  Rocky  Mountain 
region  which  have  dealt  principally  with  the  production  of  this  im- 
portant coal  field. 

The  first  systematic  work  in  this  field  was  done  in  1893-94  by 
W.  H.  Weed,  assisted  by  L.  V.  Pirsson.  In  their  published  report6 


a Relation  of  the  coal  of  Montana  to  the  older  rocks:  Tenth  Census  U.  S.,  vol.  15,  1880,  pp.  697-712. 
b Highwood  Mountains  of  Montana:  Bull.  Geol.  Soc.  America,  vol.  6,  1894-95,  pp.  389-422. 


LITERATURE. 


9 


the  topographic  and  geologic  features,  structure,  and  characteristic 
rocks  of  the  different  eruptive  centers  of  the  Highwood  Mountains 
and  vicinity  are  discussed  at  considerable  length.  In  1899  the  Fort 
Benton  folio, a which  includes  the  eastern  part  of  the  area  described, 
and  the  Little  Belt  Mountains  folio,6  which  treats  of  the  area  adjoining 
on  the  south,  both  by  Mr.  Weed,  were  published  by  the  Geological 
Survey.  During  the  past  few  years  the  glacial  geology  of  this  por- 
tion of  Montana  has  been  described  by  Warren  Uphamc  and  by 
F.  H.  H.  Calhoun. d 

Since  the  Government  irrigation  project  has  been  undertaken  in 
Sun  and  Teton  valleys,  a number  of  scientific  and  popular  articles 
have  appeared  dealing  principally  with  the  surface  waters  of  the 
district.  In  1906  an  investigation  of  the  underground  waters  of  this 
general  region  was  made  by  the  writer,  the  results  of  which  will  soon 
be  published  by  the  Geological  Survey. 

The  following  bibliography  contains  the  titles  of  the  more  important 
geologic  papers  dealing  with  this  region,  arranged  in  chronologic  order: 

Lewis  and  Clark  Expedition,  1804-1806  (Coues,  4 vols.,  1893). 

An  account  of  the  journey  up  the  Missouri  from  St.  Louis  to  the  Rocky  Mountains, 
thence  to  the  Pacific  coast.  Contains  description  of  the  region  bordering  on  the  Mis- 
souri in  the  vicinity  of  Great  Falls,  Mont.  The  falls  of  the  Missouri  were  measured 
and  described;  also  brief  mention  made  of  the  Giant  Springs. 

Hayden,  F.  V.,  Geologic  report  of  the  exploration  of  the  Yellowstone  and  Missouri 
rivers,  U.  S.  War  Dept.,  pp.  85-94.  1860. 

Contains  a chapter  on  the  geology  from  Wind  River  Mountains  to  Fort  Union  on 
Missouri  River.  Gives  description  of  a trip  down  Smith  River  and  past  the  falls  of 
the  Missouri  to  Fort  Benton,  etc.  Includes  geologic  map  of  the  area. 

Williams,  Albert,  Jr.,  Mineral  Resources  U.  S.  for  1883-84:  U.  S.  Geol.  Survey, 
pp.  52-55.  1885. 

The  Montana  coal  fields  are  described  briefly,  and  their  area  is  estimated. 

Newberry,  J.  S.,  Surface  geology  of  the  country  bordering  the  Northern  Pacific 
Railroad:  Am.  Jour.  Sci.,  3d  ser.,  vol.  30,  pp.  337-347.  1885. 

Includes  a brief  description  of  the  surface  geology  in  the  vicinity  of  Great  Falls, 
Mont.,  with  special  reference  to  glacial  drift. 

Lindgren,  Waldemar,  Eruptive  rocks:  Tenth  Census  U.  S.,  vol.  15,  pp.  719-737. 
1886. 

The  igneous  intrusions  of  the  Little  Belt  and  Highwood  mountains  are  described; 
also  the  dike  near  Sun  River,  including  its  character  and  mode  of  occurrence. 

Davis,  W.  M.,  Relation  of  the  coal  of  Montana  to  the  older  rocks:  Tenth  Census 
U.  S.,  vol.  15,  pp.  697-712.  1886. 

Includes  a description  of  the  geology  of  the  Little  Belt  and  Highwood  mountains 
and  the  plains  region  from  Fort  Benton  up  Missouri  and  Sun  rivers. 

Eldridge,  G.  H.,  Montana  coal  fields:  Tenth  Census  U.  S.,  vol.  15,  pp.  742-751. 
1886. 

Treats  of  the  coals  along  Belt  Creek,  Sand  Coulee,  and  Deep  Creek  (Smith  River), 
giving  a section  of  the  geologic  formations  at  Belt  Butte,  near  Belt.  The  coals  of  the 
Sage  Creek  area  are  described  as  a part  of  the  Judith  Basin  coal  fields. 

® Geologic  Atlas  U.  S.,  folio  55,  U.  S.  Geol.  Survey,  1899. 
b Geologic  Atlas  U.  S.,  folio  56,  U.  S.  Geol.  Survey,  1899. 
c Outer  glacial  drift:  Am.  Geologist,  vol.  34,  1904,  pp.  151-160. 

d Montana  lobe  of  the  Keewatin  ice  sheet:  Prof.  Paper,  U.  S.  Geol.  Survey  No.  50, 1906. 


10 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


Day,  David  T.,  Mineral  Resources  U.  S.  for  1885:  U.  S.  Geol.  Survey,  pp.  36-39. 
1886. 

Brief  reference  is  made  to  the  coal  production  of  the  Belt  and  Sand  Coulee  mines. 

Day,  David  T.,  Mineral  Resources  U.  S.  for  1886:  U.  S.  Geol.  Survey,  pp.  262-288. 
1887. 

Eldridge  is  quoted  in  reference  to  the  extent  and  character  of  Montana  coal  fields. 
(See  Eldridge.)  The  production  of  the  Great  Falls  region  is  given. 

Newberry,  J.  S.,  The  Great  Falls  coal  field:  School  of  Mines  Quart.,  vol.  8,  No.  4, 
p.  327.  1887. 

Gives  evidence  as  to  the  geologic  age  of  the  coal-bearing  rocks  in  the  Great  Falls 
region,  correlating  them  with  the  Kootenai  formation  of  the  Lower  Cretaceous  of 
Canada. 

Chamberlin,  T.  C.,  Rock  scorings  of  the  great  ice  invasions:  Seventh  Ann.  Rep. 
U.  S.  Geol.  Survey,  p.  77.  1888. 

Discusses  local  “mountain  wash”  from  High  wood  Mountains,  etc. 

Mortson,  0.  C.,  and  Ashburner,  Chas.  A.,  Mineral  Resources  U.  S.  for  1888: 
U.  S.  Geol.  Survey,  pp.  34-35,  289-292.  1890. 

Describes  the  occurrence,  extent,  and  chemical  character  of  iron  ores  in  the  vicinity 
of  Great  Falls,  Mont.,  pp.  34-35.  Also  refers  to  coal  areas  and  operations  in  north- 
central  Montana,  pp.  289-292. 

Swallow,  G.  C.,  Report  of  the  Montana  inspector  of  mines  for  the  six  months  end- 
ing November  30,  1889,  pp.  43-51. 

Contains  reports  on  various  coal  fields  in  Montana,  including  those  of  Cascade 
County.  Analyses  of  Sand  Coulee  coal  are  given  and  comparison  made  with  eastern 
coking  coals.  Estimates  of  the  amount  of  coal  in  Cascade  County  are  given. 

Swallow,  G.  C.,  Report  of  the  Montana  inspector  of  mines,  1890. 

Includes  reports  on  various  coal  fields  in  Montana,  making  brief  mention  of  those 
in  Cascade  County. 

Newberry,  J.  S.,  Flora  of  the  Great  Falls  coal  field:  Am.  Jour.  Sci.,  3d  ser.,  vol. 
41,  pp.  191-201.  1891. 

Describes  briefly  the  general  geology  of  the  Great  Falls  region,  and  gives  detailed 
description  of  fossil  plants  collected  near  the  mouth  of  Sun  River,  Montana. 

Parker,  E.  W.,  Mineral  Resources  IT.  S.  for  1889-90:  U.  S.  Geol.  Survey,  pp. 
228-231.  1892. 

The  coal  product  of  Montana  is  treated  by  counties  and  the  amount  applied  to 
various  uses  is  also  shown.  List  is  given  of  producing  mines  of  the  Great  Falls  region. 
Sand  Coulee  mine  is  largest  producer.  Contains  analysis  of  Sand  Coulee  coal. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1891:  U.  S.  Geol.  Survey,  pp.  269-270. 
1893. 

The  production  of  Montana  coal  mines,  including  those  in  the  Great  Falls  <.oal  field, 
is  referred  to  briefly. 

Weed,  W.  H.,  The  coal  fields  of  Montana:  Eng.  and  Min.  Jour.,  vol.  53,  pp.  520- 
522,  542-543,  1892;  vol.  55,  p.  197,  1893. 

Describes  the  geologic  occurrence  of  the  coal  beds  and  the  character  and  extent  of 
the  coal  deposits  in  various  Montana  areas,  including  Great  Falls. 

Shoemaker,  C.  S.,  Report  of  the  Montana  inspector  of  mines.  1893. 

Includes  reports  on  Cascade  County  coal  mines.  The  equipment  and  output  of 
Belt  and  Sand  Coulee  mines  are  treated  on  page  33,  and  they  are  described  and  a 
statement  of  their  production  given  on  page  86. 

Weed,  W.  H.,  Two  Montana  coal  fields:  Bull.  Geol.  Soc.  America,  vol.  3,  pp.  301- 
330.  1892.  Abstract:  Am.  Geologist,  vol.  11,  pp.  181-182.  1893. 

Describes  the  general  geology  of  the  Great  Falls  coal  field,  giving  information  con- 
cerning the  character  and  extent  of  the  coals.  The  age  of  the.  coal-bearing  rocks  is 
also  discussed. 


LITERATURE. 


11 


Wilson,  H.  M.,  American  irrigation  engineering:  Thirteenth  Ann.  Rept.  U.  S. 
Geol.  Survey,  pt.  3,  pp.  371-386.  1893. 

The  proposed  irrigation  system  of  the  Sun  River  valley  and  the  adjacent  region  is 
fully  described,  and  the  rainfall,  topography,  and  amount  of  reclaimable  land  is  dis- 
cussed. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1892:  U.  S.  Geol.  Survey,  pp.  436-438. 

1893. 

The  coal  production  of  Montana  is  given  by  counties,  and  classified  as  to  varieties — 
bituminous,  semibituminous,  and  lignite. 

Fontaine,  W.  M.,  Description  of  some  fossil  plants  from  the  Great  Falls  coal  field 
of  Montana:  Proc.  U.  S.  Nat.  Mus.,  vol.  15,  pp.  487-495.  1893. 

Gives  a description  of  the  general  character  of  the  flora,  its  age,  and  the  character- 
istics of  several  new  species. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1893:  U.  S.  Geol.  Survey,  pp.  320-322. 

1894. 

The  coal  output  of  Montana  is  given  by  counties.  Reference  is  made  to  the 
increased  activity  over  previous  years. 

Parker,  M.  S.,  Water  power  of  the  falls  of  the  Missouri,  Great  Falls,  Mont.:  Eng. 
News,  vol.  32,  p.  44.  1894. 

The  several  falls  of  the  Missouri  are  described,  and  estimates  made  of  their  water 
power.  Makes  reference  to  the  Giant  Springs  and  their  effect  on  the  river  water. 

Weed,  W.  H.,  and  Pirsson,  L.  V.,  High  wood  Mountains  of  Montana:  Bull.  Geol. 
Soc.  America,  vol.  6,  pp.  389-422.  1895. 

Describes  the  topographic  features,  geologic  structure,  and  characteristics  of  the 
rocks  of  each  eruptive  center  of  the  High  wood  Mountains.  Reference  is  also  made 
to  the  coal  at  Belt,  Mont.,  its  thickness,  character,  and  age. 

Parker,  E.  W.,  Sixteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.,4,  pp.  144-148.  1895. 

The  coals  of  Montana  are  discussed  and  reference  is  made  to  their  geologic  age. 
The  bituminous  and  lignitic  fields  are  differentiated.  Production  by  counties  is  given. 

Parker,  M.  S.,  The  Great  Falls  watey  power:  Eng.  Rec.,  vol.  31,  No.  16,  pp.  274- 
275.  1895. 

Gives  brief  description  of  the  various  falls  of  the  Missouri  near  Great  Falls,  Mont., 
with  illustrations  of  the  power  plant  at  Black  Eagle  Falls. 

Shoemaker,  C.  S.,  Report  of  the  Montana  inspector  of  mines,  1895. 

Includes  reports  of  various  coal  fields  in  Montana,  their  production,  etc.  Cascade 
County  mines  are  treated  on  p.  42. 

Parker,  E.  W.,  Seventeenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3,  pp.  454-458. 
1896. 

A condensed  report  on  Montana  coal  production  is  included. 

Parker,  E.  W.,  Eighteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  5,  pp.  551-556.  1897. 
A review  including  the  coal  production  of  Montana  by  counties,  from  1889  to  1896, 
inclusive. 

Byrne,  John,  Report  of  the  Montana  inspector  of  mines,  pp.  37-38.  1897. 

Includes  reports  on  coal  fields  of  Montana,  and  describes  Belt  and  Sand  Coulee  mines. 
Parker,  E.  W.,  Nineteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  6,  pp.  456-461. 
1898. 

A brief  review  is  given  of  production  of  coal  in  Montana,  dating  from  1889.  The 
number  of  mines  in  each  county  (in  1896),  their  output,  and  various  items  of  informa- 
tion regarding  the  production  are  included. 

Parker,  E.  W.,  Twentieth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  6,  pp.  440-443.  1899. 

Cascade  County  is  credited  with  two-thirds  of  the  entire  State  coal  production. 
Tables  of  coal  production  by  counties  are  also  included. 

Weed,  W.  H.,  Fort  Benton  folio,  Montana:  Geologic  Atlas  U.  S.,  folio  55,  U.  S.  Geol. 
Survey,  1899. 


12 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


Describes  the  surface  features,  geology,  structure,  and  history  of  the  region.  Treats 
in  considerable  detail  the  mineral  resources,  including  coal,  gold,  and  silver.  Con- 
tains topographic,  geologic,  economic,  and  structural  maps,  also  columnar  sections. 
Parker,  E.  W.,  Twenty-first  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  6,  pp.  468-471. 

1900. 

Includes  brief  classified  statistical  tables  of  Montana  coal  production  for  1898. 
States  that  a large  proportion  of  coal  is  machine  mined. 

Byrne,  John,  Report  of  the  Montana  inspector  of  mines:  Twelfth  Annual  Report, 
pp.  53-54.  1900. 

Includes  reference  to  workings  and  output  of  coal  mines  at  Belt,  Stockett,  and  Sand 
Coulee,  Mont. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1900:  U.  S.  Geol.  Survey,  pp.  406-408. 

1901. 

Statistics  are  given  of  coal  production  in  Montana  for  1899.  That  of  1900  is  stated 
to  be  the  largest  in  the  history  of  the  State,  amounting  to  1,661,775  short  tons;  value 
$2,713,707.  Sixty-three  per  cent  of  the  total  production  was  machine  mined. 

Storrs,  L.  S.,  The  Rocky  Mountain  coal  fields:  Twenty-second  Ann.  Rept.  U.  S. 
Geol.  Survey,  pt.  3,  1901,  pp.  415-471.  1902. 

Includes  discussion  of  the  Montana  coal  fields,  mentioning  briefly  the  Great  Falls 
coal  field. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1901:  U.  S.  Geol.  Survey,  pp.  401-403. 

1902. 

Gives  tables  of  Montana  coal  production.  During  1901  the  Sand  Coulee  mines 
were  practically  abandoned,  decreasing  the  output  of  Cascade  County  333,988  tons. 

Storrs,  L.  S.,  Eighth  Rept.  Montana  Bureau  Agr.,  Labor,  and  Industry,  pp.  374- 
382.  1902. 

Coal  statistics  for  the  State  are  given,  and  Storrs  is  quoted  in  reference  to  the  extent 
and  distribution  of  Montana  coal  fields. 

Willis,  Bailey,  Stratigraphy  and  structure,  Lewis  and  Livingstone  ranges,  Montana: 
Geol.  Soc.  Am.,  vol.  13,  pp.  305-352.  1902. 

Describes  the  physiography,  the  occurrence,  and  character  of  the  Algonkian,  Car- 
boniferous, Cretaceous,  and  Pleistocene  formations,  and  the  geologic  structure  of  the 
general  region. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1902:  U.  S.  Geol.  Survey,  pp.  396-398. 

1903. 

Tabulated  statistics  of  Montana  coal  production  are  given. 

Rowe,  J.  P.,  Some  Montana  coal  fields:  Am.  Geologist,  vol.  32,  pp.  369-380.  1903. 
Describes  by  counties  the  bituminous,  semibituminous,  and  lignite  coals  of  Montana, 
giving  briefly  their  geologic  age  and  distribution. 

Rowe,  J.  P.,  Some  volcanic  ash  beds  in  Montana:  Bull.  Montana  Univ.  No.  17 
(geol.  ser.,  No.  1).  1903. 

Discusses  the  origin  and  physical  and  chemical  properties  of  volcanic  ash  in  Montana, 
describing  by  counties  its  characteristics,  geologic  position,  and  general  distribution. 
A number  of  illustrations  are  introduced,  showing  the  microscopic  character  of  the 
volcanic  ash,  leaves  found  in  the  deposits,  and  thickness  and  character  of  beds. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1903:  U.  S.  Geol.  Survey,  pp.  484-487. 

1904. 

Contains  brief  review  of  coal-mining  conditions  in  Montana  as  compared  with  pre- 
vious years,  and  gives  statistics  of  the  coal  output  of  the  State. 

Newell,  F.  IL,  Third  Ann.  Rept.  U.  S.  Reclamation  Service,  pp.  307-313.  1904. 

Discusses  the  proposed  irrigation  project  of  the  Sun  and  Teton  river  district,  and 
describes  the  water  supply  available  from  streams  and  storage  reservoirs,  also  the  ter- 
ritory which  can  be  irrigated. 

Leiberg,  J.  C.,  Forest  conditions  in  the  Little  Belt  Mountains  Forest  Reserve, 
Mont.,  and  the  Little  Belt  Mountains  quadrangle:  Prof.  Paper  U.  S.  Geol.  Survey  No. 
30,  1904. 


LITERATURE. 


13 


The  surface  waters  of  the  region  and  their  relation  to  agricultural,  grazing,  and  forest 
lands  are  included  in  the  discussion. 

Stockett,  Lewis,  A bituminous  coal  breaker  in  Montana:  Min.  World,  vol.  20,  March 
26,  1904. 

Gives  section  and  analysis  of  the  coal  bed  mined  at  Stockett,  Mont.,  and  a detailed 
description  of  the  coal  breaker  use^l  by  the  company. 

Upham,  Warren,  Outer  glacial  drift:  Am.  Geologist,  vol.  34,  pp.  151-160.  1904. 

Discusses  the  glacial  drift  of  the  northwestern  States,  including  Montana.  Ref- 
erence is  made  to  the  effect  which  the  glaciation  had  on  the  course  of  Missouri  River. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1904:  U.  S.  Geol.  Survey,  pp.  512-515. 

1905. 

Includes  a discussion  of  the  various  Montana  coal  fields,  their  geologic  age  and  im- 
portance. The  production  by  counties  is  given,  and  the  State  output  tabulated  from 
1880,  the  year  of  first  reported  production. 

Savage,  H.  N.,  Fourth  Ann.  Rept.  U.  S.  Reclamation  Service,  pp.  222-224.  1905. 

Includes  report  of  surveys  and  lands  to  be  irrigated  by  the  Sun  River  project. 

Pirsson,  L.  V.,  Petrographic  province  of  central  Montana:  Am.  Jour.  Sci.,  4th  ser., 
vol.  20,  pp.  35-49.  1905. 

Treats  of  the  various  igneous  occurrences  in  the  region  of  Belt  and  Highwood  moun- 
tains, including  a description  of  the  porphyry  of  the  Wolf  Butte  and  Square  Butte  (of 
Highwood  Mountains)  laccoliths,  and  dike  near  the  Highwoods  on  Williams  Creek. 

Rowe,  J.  P.,  Montana  gypsum  deposits:  Am.  Geologist,  vol.  35,  pp.  104-113.  1905. 

The  gypsum  deposits  are  classified  by  localities,  as  the  north,  middle,  and  south 
fields.  The  middle  field  includes  Cascade  and  Fergus  counties.  Includes  descrip- 
tion of  Stucco  mill  on  Belt  Creek,  giving  location  and  age  of  deposits. 

Rowe,  J.  P.,  The  Montana  coal  fields:  Min.  Mag.,  vol.  11,  pp.  241-250.  1905. 

Discusses  the  production  and  value  of  coal  from  various  fields  in  Montana,  including 
the  Great  Falls  coal  field.  Treats  of  present  and  future  development  of  Belt  and  Sand 
Coulee  mining  districts,  including  geologic  distribution  of  Montana  coals  by  counties. 
Boiler  tests  and  chemical  analysis  of  Belt  coal  are  also  given. 

Parker,  E.  W.,  Mineral  Resources  U.  S.  for  1905:  U.  S.  Geol.  Survey,  pp.  631-633. 

1906. 

Statistics  are  given  of  the  Montana  coal  output,  also  a short  discussion  of  the  different 
fields. 

Walsh,  William,  Report  of  the  Montana  inspector  of  mines,  pp.  29-38.  1906. 

Includes  reports  of  Cascade  County  mines,  their  development,  production,  etc. 

Calhoun,  F.  H.  H.,  The  Montana  lobe  of  the  Keewatin  ice  sheet:  Prof.  Paper 
U.  S.  Geol.  Survey  No.  50,  1906. 

Describes  briefly  the  surface  features  and  geology  along  the  terminal  moraine  of  the 
Keewatin  ice  sheet  in  Montana.  Contains  detailed  description  of  the  glacial  deposits 
and  discusses  the  effects  of  glaciation  of  the  region  on  the  course  of  Missouri  River. 

Rowe,  J.  P.,  Montana  coal  and  lignite  deposits:  Bull.  Montana Univ.  No.  37  (geol. 
ser.  No.  2).  1906. 

Describes  Montana  coals  by  counties.  Contains  a bibliography  of  literature  bearing 
on  the  subject. 

Fisher,  C.  A.,  Great  Falls  coal  field:  Bull.  U.  S.  Geol.  Survey  No.  316.  1907. 

Describes  briefly  the  coals  of  the  Great  Falls  region,  giving  their  location,  topo- 
graphic relation,  and  geologic  occurrence.  Detailed  description  of  the  deposit  is 
given  and  representative  sections  introduced.  The  present  development  of  the  vari- 
ous basins  within  the  field  is  treated,  and  the  quality  of  the  coal  is  briefly  described, 
including  a number  of  ultimate  analyses  of  representative  coals  in  the  field. 

Fisher,  C.  A.,  Southern  extension  of  the  Kootenai  and  Montana  coal-bearing  for- 
mations in  northern  Montana:  Econ.  Geol. , vol.  3,  pp.  77-99.  1908. 


14  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

Describes  the  Kootenai  formation  in  the  vicinity  of  Great  Falls,  Mont.,  tracing  it 
southward  across  the  Montana- Wyoming  State  line  into  the  Bighorn  basin,  where  it  is 
correlated  with  the  Cloverly  formation.  The  subdivisions  of  the  Montana  group  in 
northern  Montana,  as  first  worked  out  by  Stanton  and  Hatcher,  are  also  traced  south- 
ward to  the  State  line.  The  occurrence  of  coal  in  these  formations  at  different  locali- 
ties throughout  the  area  treated  is  given. 

Fisher,  C.  A.,  Geology  and  water  resources  of  the  Great  Falls  region,  Montana: 
Water  Supply  Paper  No.  221,  U.  S.  Geol.  Survey,  1908. 

A brief  treatment  of  the  general  geology  of  the  region  is  given,  with  special  reference 
to  the  prospects  for  the  occurrence  of  underground  water.  The  surface  waters  are  also 
described,  including  their  present  and  proposed  uses  for  irrigation,  waterpower,  etc. 

TOPOGRAPHY. 

RELIEF. 

The  area  treated  in  this  report  presents  a considerable  variety  of 
geographic  features,  all  of  which  have  a direct  or  indirect  bearing  on 
the  development  of  the  coal  resources  of  the  Great  Falls  field. 
The  area  lies  within  a zone  which  is  transitional  between  plains 
and  mountain  topography,  including  portions  that  present  features 
characteristic  of  both  provinces.  Its  salient  features  are  broad, 
gently  sloping  plateaus  bordering  the  adjacent  mountain  ranges. 
These  plateaus  are  traversed  by  numerous  mountain  streams,  which 
flow  through  valleys  that  are  deep  and  relatively  narrow  in  the 
central  portion  of  the  district,  but  that  become  wide  and  open  on 
the  plains  to  both  the  east  and  the  west.  Along  the  southern  margin 
of  the  area,  from  Smith  River  to  the  eastern  end  of  the  field,  the  sur- 
face of  the  plains  rises  gradually  by  sloping  plateaus,  culminating 
in  a zone  of  high,  hilly  country  bordering  the  Little  Belt  Mountains, 
which  lie  to  the  southward.  East  of  Belt  Creek  and  north  of  the 
area  described  the  Highwood  Mountains,  a cluster  of  isolated  peaks, 
rise  abruptly  above  the  plains  to  an  altitude  of  6,700  feet.  Between 
the  Highwood  and  Little  Belt  mountains  there  is  a divide  locally 
known  as  the  Otter  Creek  divide,  whose  altitude  at  its  lowest  point 
is  about  4,500  feet.  The  country  east  of  this  divide  is  drained  by 
Arrow  Creek  and  its  tributaries;  that  to  the  west  by  Belt  Creek  and 
its  largest  affluent,  Otter  Creek,  from  which  the  divide  derives  its 
name. 

The  range  of  altitude  within  the  field  is  moderate.  The  highest 
points  occur  along  the  base  of  the  Little  Belt  Mountains,  where  the 
more  prominent  summits  rise  to  an  altitude  of  about  5,500  feet, 
while  the  lowest  portion  of  the  field  lies  along  Missouri  River,  below 
Big  Falls,  where  the  altitude  is  about  3,000  feet  above  sea  level. 
The  average  altitude  of  the  region  is  between  3,500  and  4,000  feet, 
and  the  extreme  variation  in  altitude  for  any  given  localit}^  is  about 
1,300  feet  in  a horizontal  distance  of  1^  miles.  This  difference  in 
elevation  occurs  between  Belt  Creek  and  the  summit  of  Belt  Butte. 


TOPOGRAPHY. 


15 


In  the  plains  province  the  relative  altitudes  of  the  valley  bottoms 
and  the  summits  of  the  bordering  plateaus  range  from  300  to  600 
feet. 

East  of  the  low  divide  between  the  Highwood  and  Little  Belt 
mountains  the  country  slopes  gradually  northeastward  toward 
Missouri  River.  It  is  traversed  by  several  streams  draining  the  north- 
eastern slope  of  Little  Belt  Mountains.  These  streams  flow  through 
relatively  wide  open  valleys  bordered  by  gravel-capped  terraces  of 
different  elevation.  Stanford  Butte,  a prominent  ridge  between 
Running  Wolf  and  Surprise  creeks,  is  capped  by  a remnant  of  an 
ancient  terrace,  and  to  the  north  and  east  of  this  ridge  gravel-capped 
plateaus  at  lower  levels  occupy  all  the  interstream  spaces.  Toward 
the  Little  Belt  Mountains  the  gravel-capped  terraces  give  way  to 
prominent  hogback  ridges  formed  by  the  sandstone  members  of  the 
Ellis  and  Kootenai  formations,  which  extend  in  an  irregular  line 
along  the  base  of  the  mountains.  Skull  Butte,  a low  dome-shaped 
uplift  about  6 miles  south  of  Stanford,  rises  nearly  200  feet  above 
the  surrounding  region.  It  is  considerably  dissected  about  the 
periphery  and  in  the  center  by  numerous  small  streams,  some  of 
which  expose  the  coal  bed  of  the  Kootenai  formation,  which  encircles 
this  uplift.  South  of  Skull  Butte  there  are  a number  of  prominent 
ridges  with  long  gradual  slopes  to  the  north  and  bold  escarpments  to 
the  south,  overlooking  valleys  which  have  been  excavated  in  the 
softer  shale  of  the  Quadrant  formation. 

Throughout  the  area  east  of  the  low  divide  connecting  the  High- 
wood  and  Little  Belt  mountains  the  valleys  leading  into  the  moun- 
tains are  wide  and  open  on  the  plains,  but  toward  the  foothill  zone 
they  decrease  in  width,  deepen,  and  branch  into  many  canyon 
tributaries  which  cut  the  upturned  edges  of  the  coal-bearing  Kootenai 
rocks,  thus  exposing  the  coal  bed  at  many  places.  These  numerous 
small  valleys  lead  from  the  zone  of  coal  outcrop  in  the  higher  hogback 
ridges  down  to  the  more  nearly  level  plains  region  where  the  main 
line  of  the  Billings  and  Northern  Railroad  has  been  constructed, 
and  thus  afford  an  easy  approach  to  the  coal. 

Broadly  viewed,  the  country  between  Otter  Creek  divide  and 
Missouri  River,  which  includes  the  largest  area  in  the  Great  Falls  coal 
field  underlain  by  workable  coal,  is  a high  plateau  sloping  gently 
northward,  and  deeply  dissected  by  numerous  canyons.  Otter, 
Belt,  and  Boxelder  creeks,  Sand  Coulee,  and  Smith  River  are  the 
principal  streams  traversing  this  area.  All  of  these  except  Boxelder 
Creek  flow  through  deep,  narrow  valleys  which  cut  through  and 
expose  the  coal,  and  along  them,  owing  to  the  general  accessibility 
of  the  beds,  the  principal  development  of  the  coal  resources  of  the 
Sand  Coulee  area  has  taken  place.  The  altitude  of  the  plateau 
varies  from  3,500  feet  along  Missouri  River  to  4,500  feet  or  more 


16  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

along  the  southern  border  of  the  area.  The  difference  in  altitude 
between  valley  bottom  and  plateau  summit  in  the  northern  part  of 
the  district  is  200  to  400  feet,  but  toward  the  mountains  this  difference 
increases  to  over  600  feet.  The  streams  of  this  district  all  flow  in  a 
northerly  direction  except  three  of  the  larger  tributaries  of  Smith 
River — Boston,  Ming,  and  Goodwin  coulees — which  flow  nearly  west. 
Sand  Coulee,  which  is  formed  by  the  confluence  of  a number  of 
canyon  tributaries  6 miles  southeast  of  Stockett,  continues  north- 
ward for  several  miles  to  a point  when  it  turns  sharply  to  the  west, 
and  for  the  remainder  of  its  course  it  meanders  through  a wide, 
flat-bottomed  valley  formed  by  the  preglacial  erosion  of  Missouri 
River. 

West  of  the  Missouri  and  south  of  Sun  River  the  surface  rises  in 
successive  plateaus  to  the  west.  The  lowest  of  these,  which  lies 
north  of  Ulm  station  and  comprises  what  is  locally  known  as  Ulm 
Bench,  has  an  altitude  of  about  3,650  feet.  On  the  west  side  of 
Ulm  Bench  there  is  a low  saddle  separating  it  from  a higher  plateau, 
only  a small  portion  of  which  is  included  within  the  area  described. 
North  of  Sun  and  Missouri  rivers  there  is  a high  plateau  region 
which  farther  west  is  deeply  dissected  by  the  valley  of  Muddy  Creek. 
East  of  Muddy  Creek  only  the  southern  edge  of  this  plateau  is  included 
within  the  held.  It  extends  eastward  as  a line  of  prominent  bluffs 
north  of  Great  Falls,  terminating  in  a group  of  ridges  and  buttes  of 
which  Black  Butte  is  a conspicuous  outlier. 

DRAINAGE. 

The  Great  Falls  held,  being  located  along  the  base  of  the  Rocky 
Mountain  front  range,  is  traversed,  especially  in  its  western  half,  by 
a number  of  relatively  large  mountain  streams,  some  of  which  have 
been  important  factors  in  the  industrial  development  of  the  district. 
The  eastern  half  of  the  area  contains  no  large  rivers,  but  is  drained, 
as  previously  stated,  by  numerous  small  mountain  streams  which 
how  northeastward,  entering  the  Missouri  by  way  of  Judith  River. 

MISSOURI  RIVER. 

The  principal  stream  of  the  district  is  Missouri  River.  It  enters 
the  held  near  Cascade,  and  hows  in  a northerly  direction  to  the 
vicinity  of  Great  Falls,  where  it  pursues  a more  easterly  course,  con- 
tinuing thus  to  the  border  of  the  held.  The  portion  of  the  stream 
above  Great  Falls  hows  in  a meandering  course  through  a wide,  open 
valley,  but  that  below  this  point  occupies  a narrow  valley  bordered 
by  precipitous  bluffs,  passing  over  a number  of  cataracts  known  as 
the  Great  Falls  of  Missouri  River.  At  present  only  one  of  these  falls, 
Black  Eagle,  the  uppermost  of  the  series,  is  utilized  for  the  develop- 
ment of  power.  The  drainage  area  of  the  Missouri  at  Cascade,  Mont., 


TOPOGRAPHY. 


17 


is  estimated  as  18,295  square  miles,  and  the  flow  of  the  river  ranges 
from  2,000  to  22,000  second-feet.  Its  largest  tributaries  from  the 
south  are  Smith  River  and  Belt  Creek,  and  from  the  west  Sun  River. 
A number  of  medium  and  large-sized  intermittent  streams  with 
relatively  large  drainage  areas  enter  the  river  from  either  side. 
Bird  Creek,  Castner  Coulee,  Sand  Coulee  and  its  tributaries,  Boxelder 
Creek,  and  Red  Coulee  enter  from  the  south,  and  Little  Muddy 
Creek  enters  from  the  west.  The  city  of  Great  Falls  and  the  Boston 
and  Montana  smelters  are  located  on  Missouri  River,  and  the  Great 
Northern  Railway  has  been  built  up  its  valley  through  the  Big  Belt 
Mountains,  connecting  Great  Falls  with  the  large  mining  centers 
of  Butte  and  Anaconda. 

SUN  RIVER. 

Sun  River  rises  high  in  the  Lewis  Range  and  joins  the  Missouri  at 
Great  Falls.  Only  the  lower  course  of  the  river,  however,  is  included 
within  this  field.  The  main  stream  is  formed  by  the  union  of  the 
north  and  south  forks  of  Sun  River,  which  occurs  about  3 miles 
below  Augusta,  a town  located  a few  miles  east  of  the  base  of  the 
Lewis  Range,  beyond  the  limits  of  the  field.  The  principal  tributary 
of  Sun  River  from  the  north  within  the  area  described  is  Muddy 
Creek,  which  drains  the  high  plateau  between  Sun  and  Teton  rivers, 
emptying  into  the  latter  near  Vaughn.  It  is  an  intermittent  stream 
of  minor  importance. 

SMITH  RIVER. 

Smith  River  has  its  source  far  to  the  southeast,  in  the  vicinity  of 
Castle  Mountains,  and  flows  northwest,  draining  the  highland  between 
the  Big  and  Little  Belt  mountains.  It  enters  the  area  described 
near  the  center  of  the  south  line  of  T.  17  X.,  R.  3 E.,  and,  flowing 
in  a northeasterly  direction,  joins  Missouri  River  at  a point  near  Ulm. 
Within  the  district  the  stream  flows  in  a meandering  course  through 
a deep  and  moderately  narrow  valley,  which  exposes  high  in  its  bluffs 
on  either  side  the  workable  coal  bed  of  the  Kootenai  formation 
throughout  Tps.  17  N.,  Rs.  2 and  3 E.  Smith  River  has  a flow  ranging 
from  about  50  to  over  400  second-feet;  its  largest  tributary  is  Hound 
Creek,  which  joins  it  from  the  west  near  Orr  post-office.  The  valley 
of  Hound  Creek  also  exposes  the  workable  coal  of  the  lower  part  of 
the  Kootenai  for  about  1 mile  above  its  mouth,  and  the  largest  mine 
in  the  Smith  River  district  is  located  on  this  tributary,  in  the  SW.  \ 
sec.  24,  T.  17  N.,  R.  2 E.  Hound  Creek,  a vigorous  mountain  stream 
having  a continuous  flow,  drains  the  northern  end  of  the  Big  Belt 
Mountains,  some  of  its  tributaries  extending  far  up  the  slopes  of 
that  range.  From  the  east  three  intermittent  streams  enter  Smith 
River — Boston,  Ming,  and  Goodwin  coulees.  In  the  upper  part  of 
Ming  Coulee,  in  the  vicinity  of  Eden,  the  valley  exposes  the  coal 
54937— Bull.  356—09 2 


18 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


measures,  and  here  a number  of  small  mines  have  been  opened. 
The  same  is  true  in  the  upper  part  of  Boston  Coulee.  Smith  River 
Valley  and  its  principal  tributaries,  Ming  and  Boston  coulees  and 
Hound  Creek,  furnish  a valuable  means  of' access  to  the  coals  of  this 
little-developed  portion  of  the  Great  Falls  coal  field.  The  large  flow 
of  water  in  Smith  River  is  also  an  important  consideration  in  the 
development  of  this  coal  district,  for  the  percentage  of  impurities 
present  in  the  coal  is  sufficient  to  render  washing  necessary  before 
it  can  be  successfully  placed  on  the  market.  In  neither  Boston  nor 
in  Ming  coulee  is  there  sufficient  water  to  wash  the  coals  that  could 
be  mined  from  them,  but  the  impurities  might  be  removed  by  a dry- 
washer  process  such  as  is  now  employed  at  Stockett. 

BELT  CREEK. 

Belt  Creek  rises  in  the  northern  part  of  the  Little  Belt  Mountains, 
flows  northward  across  the  central  part  of  the  district,  draining  the 
territory  west  of  the  Highwood  Mountains,  and  enters  the  Missouri 
about  12  miles  northeast  of  Great  Falls.  It  flows  through  a valley 
about  300  feet  deep,  which  has  a width  varying  from  one-half  to 
three-fourths  of  a mile.  In  the  vicinity  of  the  town  of  Belt,  where 
the  valley  crosses  the  area  underlain  by  coal,  it  exposes  in  the  bluffs  on 
either  side,  a short  distance  above  the  valley,  beds  of  coal  of  workable 
thickness,  thus  producing  favorable  conditions  for  the  development 
of  the  deposits.  A number  of  mines  are  located  there,  including  the 
Anaconda  Copper  Mining  Company’s  mine,  one  of  the  largest  in  the 
Great  Falls  coal  field. 

Belt  Creek  is  a vigorous  mountain  stream  which  carries  a large 
flow  of  water  throughout  all  seasons  of  the  year,  especially  in  its 
upper  course,  but  at  the  town  of  Belt  all  this  water  sinks  to  an  under- 
flow during  the  late  summer  months,  leaving  the  stream  bed  dry. 
This  loss  is  due  principally  to  the  fact  that  the  valley  floor  here 
consists  of  soft,  porous  sandstones,  into  which  the  water  passes 
readily.  From  a point  a short  distance  below  the  town  of  Belt  to 
its  mouth  the  stream  has  a small  but  continuous  flow.  A view  of 
the  dry  bed  at  Belt  is  shown  in  PI.  III.  The  sinking  of  the  flow  of 
Belt  Creek  at  Belt  is  a disadvantageous  feature  from  a coal-mining 
point  of  view,  for  it  renders  it  necessary  to  sink  wells  in  the  valley 
in  order  to  obtain  a sufficient  amount  of  water  to  wash  the  impurities 
from  the  coal. 

The  principal  tributaries  of  Belt  Creek  are  Otter  Creek  from  the 
east  and  Neel  Creek  from  the  west.  Otter  Creek  rises  on  the  northern 
slope  of  Little  Belt  Mountains,  and,  flowing  northwest,  enters 
Belt  Creek  about  1 mile  above  Armington.  It  carries  considerable 
water  derived  from  snow  on  the  mountains  and  from  springs  along 
its  course.  Neel  Creek  is  a much  smaller  stream,  having  an  inter- 
mittent flow.  In  the  lower  part  of  the  valley  of  Neel  Creek  coal  of 


BULLETIN  NO.  356 


DRY  BED  OF  BELT  CREEK,  NEAR  BELT,  MONT. 


TOPOGRAPHY. 


19 


workable  thickness  is  exposed.  That  part  of  Otter  Creek  Valley 
which  lies  between  Spion  Kop  and  Nollar’s  mine  crosses  an  area 
underlain  by  valuable  coal  deposits,  but  in  the  center  of  this  area 
the  valley  is  not  cut  sufficiently  deep  to  expose  the  coal,  which, 
however,  could  be  easily  reached  by  shafting.  The  favorable  location 
of  this  valley  with  respect  to  the  limits  of  the  coal  area  offers  a 
valuable  means  of  access  to  the  deposits. 

OTHER  SMALL  STREAMS. 

The  area  between  Belt  Creek  and  Smith  River  is  drained  by 
Boxelder  Creek  and  Sand  Coulee.  Boxelder  Creek  rises  high  on  the 
plateaus  about  3 miles  west  of  Riceville,  flows  northward  in  a 
direction  roughly  parallel  to  Belt  Creek,  and  enters  the  Missouri 
about  9 miles  east  of  Great  Falls.  It  carries  only  a small  flow  of 
water,  and  its  valley  in  the  upper  part,  where  coal-bearing  rocks 
occur,  is  not  cut  sufficiently  deep  to  expose  the  coal;  hence  it  is  not 
an  important  factor  in  the  development  of  this  part  of  the  Great 
Falls  coal  field.  Sand  Coulee,  an  intermittent  stream  with  a large 
drainage  area,  is  formed  by  the  union  of  several  small  canyon  tribu- 
taries southeast  of  Stockett.  It  continues  northward  to  a point  about 
6 miles  below  Stockett,  where  it  makes  a sharp  turn  to  the  west  and 
meanders  through  a wide,  level-floored  valley  for  about  7 miles, 
entering  Missouri  River  about  4 miles  above  Great  Falls.  This 

O 

intermittent  drainageway,  especially  in  its  upper  course,  and  its 
tributaries  from  the  west,  Straight  and  Giffen  coulees,  have  deep 
narrow  valleys,  which  cut  and  expose  the  coal-bearing  zone  of  the 
Kootenai  formation,  thus  producing  favorable  conditions  for  develop- 
ment. It  is  in  the  valleys  of  these  intermittent  streams,  where  the 
towns  of  Stockett  and  Sand  Coulee  are  located,  that  the  greatest  coal 
mining  activity  has  taken  place. 

East  of  Otter  Creek  there  is  a prominent  ridge  that  forms  a low 
divide  between  Highwood  and  Little  Belt  Mountains.  The  drainage 
to  the  east  of  this  divide,  as  previously  stated,  is  all  to  the  northeast, 
into  Arrow  Creek,  a small  tributary  of  the  Missouri  entering  the  latter 
a short  distance  above  the  mouth  of  Judith  River.  Arrow  Creek, 
which  has  its  source  on  the  southern  slope  of  Highwood  Mountains, 
flows  eastward,  passing  out  of  this  district  in  T.  18  N.,  R.  11  E.  Its 
principal  affluents  are  Surprise  and  Running  Wolf  creeks,  the  former 
having  its  source  at  the  base  of  Wolf  Butte  and  pursuing  a north- 
easterly course.  Running  Wolf  Creek  rises  higher  up  the  slopes  of 
the  Little  Belt  Mountains  farther  to  the  southeast,  and  flows  north- 
eastward past  Stanford  Butte.  East  of  Running  Wolf  Creek  several 
small  branches  cross  the  extreme  southeast  corner  of  the  district 
and  enter  Judith  River.  These  are  Skull,  Willow,  and  Sage  creeks, 
all  of  which,  as  previously  stated,  expose  in  their  upper  courses  work- 
able beds  of  coal. 


20  GEOLOGY  OF  GllEAT  FALLS  GOAL  FIELD,  MOMAtfA. 

CULTURE, 

Settlement  in  the  Great  Falls  field,  as  elsewhere*  is  determined  by 
geologic  and  climatic  Conditions,  Along  all  the  larger  stream  valleys 
where  surface  water  for  irrigation  purposes  is  available  settlements 
are  numerous,  while  much  of  the  upland  and  grazing  districts  is 
thinly  populated.  On  the  higher  slopes  bordering  the  mountains  in 
the  zone  of  increased  rainfall  there  are  many  small  farms,  some  of 
which  are  among  the  best  improved  places  in  the  district. 

There  is  one  relatively  large  town,  three  medium-sized  coal-mining 
towns,  and  a number  of  smaller  trading  points.  Great  Falls,  a town  of 
18,000  inhabitants  and  a thriving  business  center,  is  located  on 
Missouri  River  near  the  north-central  portion  of  the  field.  While  at 
present  none  of  its  railroad  lines  are  transcontinental,  they  are  the 
most  important  connecting  lines  between  the  Great  Northern  and  the 
Northern  Pacific,  and  when  the  Billings  and  Northern  is  completed  it 
will  open  up  a new  transcontinental  route  through  Great  Falls  to  the 
northwest  coast.  At  the  present  time  railroads  extend  in  four 
directions  from  Great  Falls“one  southwest  to  Helena  and  Butte; 
another  northwest  to  Havre,  a small  town  on  the  main  line  of  the 
Great  Northern;  a third,  the  Montana  and  Great  Northern,  north- 
west to  Shelby  Junction;  and  a fourth,  the  Neihart  branch  of  the  same 
road,  southeast  to  Neihart.  The  last  named  is  connected  with 
Stockett  and  Sand  Coulee,  two  of  the  larger  coal-mining  camps,  by 
a short  branch  line  from  Gerber  station.  The  Boston  and  Montana 
Consolidated  Copper  and  Silver  Mining  Company’s  smelters  and 
refineries  are  located  at  Great  Falls,  as  is  also  the  Royal  Milling 
Company’s  plant  and  a number  of  smaller  business  enterprises.  The 
ore  handled  at  the  smelters  comes  from  Butte  and  Anaconda;  this, 
together  with  the  coal  and  limestone  used  in  the  operation  of  the  plant 
makes  a relatively  large  freight  traffic  for  Great  Falls,  while  it  also  fur- 
nishes employment  for  a large  number  of  men. 

Belt,  one  of  the  largest  coal  mining  towns  in  the  district,  has  a 
population  of  about  1,000,  composed  mainly  of  employees  of  the 
Anaconda  Copper  Mining  Company,  the  largest  coal-mine  operator  at 
the  place.  It  is  located  on  Belt  Creek,  about  25  miles  southeast  of 
Great  Falls,  on  the  Neihart  branch  of  the  Great  Northern  Railway, 
and  is  the  oldest  coaling  town  in  this  region.  About  10  miles  south- 
west of  Belt  and  nearly  20  miles  from  Great  Falls  are  the  two  coal- 
mining towns  of  Stockett  and  Sand  Coulee.  Stockett,  which  has 
a population  of  about  800,  composed  largely  of  coal  miners  employed 
by  the  Cottonwood  Coal  Company,  one  of  the  two  largest  coal  min- 
ing companies  operating  in  the  district,  is  located  on  East  Fork  of 
Sand  Coulee.  Sand  Coulee,  about  2\  miles  northwest  of  Stockett,  is 
a smaller  mining  town  of  about  400  people.  It  is  situated  in  Cotton- 
wood Coulee,  a branch  of  Sand  Coulee,  and  owes.its  existence  mainly 


U.  8.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  350  PL.  IV 


COLUMNAR  SECTIONS  OF  THE  STRATIGRAPHY  ALONG  BELT  CREEK  VALLEY. 

(Columns  are  numbered  from  left  to  right.) 

1,  West  side  of  Belt  Creek,  1 mile  north  of  Goodman  siding;  2,  east  side  of  Belt  Creek,  2£  miles  north  of 
laoodman  stding;  3,  west  side  of  Belt  Creek,  one-eighth  mile  above  mouth  of  Otter  Creek;  4,  east  side 
of  Belt  Creek,  one-eighth  mile  below  mouth  of  Otter  Creek;  5,  east  side  of  Belt  Creek,  one-half  mile 
above  Belt;  6,  east  side  of  Belt  Creek  at  Belt;  7,  west  side  of  Belt  Creek  at  Belt. 


V!  ■ vr'jjuc: 


v.  ■ ■ 


} 

: . - - 


■ . u 


STRATIGRAPHY. 


21 


to  the  Nelson  and  Gerber  coal  companies,  which  are  operating  at  this 
place. 

The  remainder  of  the  towns  within  the  district  are  supported 
mainly  by  a ranch  population. 

There  are  no  towns  along  Missouri  River  below  Great  Falls  within 
the  area  described,  but  above  that  town  there  are  two  small  stations, 
Ulm  and  Cascade.  The  latter,  located  near  the  base  of  the  Big  Belt 
Mountains,  has  a population  of  about  200,  and  is  supported  by  a large 
ranch  trade  along  either  side  of  the  river. 

About  2 miles  above  the  mouth  of  Smith  River  there  is  a post-office 
known  as  Truly,  and  farther  up  the  river  there  was  another  known  as 
Orr,  which  has  recently  been  discontinued. 

In  Belt  Creek  Valley,  about  2 miles  above  Belt,  is  the  small  town  of 
Armington,  which  is  situated  at  the  junction  of  the  Billings  and 
Northern  Railroad  and  the  Neihart  branch  of  the  Great  Northern. 
It  is  mainly  a small  railroad  town,  which  receives  a portion  of  the 
ranch  trade  of  the  surrounding  country.  Along  the  Billings  and 
Northern  Railroad  there  are  a number  of  new  towns  and  sidings? 
located  at  intervals  of  about  6 miles.  These  are  Reinsford,  Spion  Kop, 
Geyser,  Stanford,  and  Windham.  Old  Stanford  and  Old  Geyser? 
which  are  located  at  some  little  distance  from  the  new  town  sites 
bearing  these  names,  are  important  trading  points  for  a large  ranch 
district  along  Arrow,  Skull,  Running  Wolf,  and  Sage  Creek  valleys. 

DESCRIPTIVE  GEOLOGY. 

STRATIGRAPHY. 

GENERAL  OUTLINE . 

The  surface  formations  throughout  the  area  to  which  this  report 
relates  consist  mainly  of  sedimentary  rocks  and  igneous  intrusives  in 
the  form  of  dikes  and  laccoliths,  the  intrusives  being  especially  abun- 
dant throughout  that  part  of  the  field  bordering  the  adjacent  mountain 
ranges.  The  strata  lie  in  general  nearly  horizontal,  dipping  at  a 
relatively  small  angle  to  the  north  and  east,  away  from  the  mountains 
and  toward  the  plains.  Throughout  most  of  the  Great  Falls  field  the 
rocks  lie  apparently  flat,  but  on  closer  examination  they  are  found  to 
be  gently  folded  into  a series  of  shallow  synclines  and  low  anticlines. 
These,  however,  are  scarcely  perceptible  to  the  casual  observer,  being 
revealed  only  by  careful  examination  of  the  beds  exposed  along  the 
sides  of  some  of  the  valleys.  The  rocks  are  representative  of  Car- 
boniferous, Jurassic,  Cretaceous,  Tertiary,  and  Quaternary  systems. 
The  distribution  of  the  formations  is  shown  on  the  geologic  map 
(PI.  I),  and  their  stratigraphy  and  structural  relations  are  illustrated 
in  the  columnar  and  cross  sections  shown  on  PL  IV  and  PI.  VII. 
The  table  on  pages  22-23  shows  the  age,  order,  characteristic  features, 
thickness,  distribution,  stratigraphic  relations,  and  economic  impor- 
tance of  the  formations. 


22 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


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STRATIGRAPHY. 


23 


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8 


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80  to  120. 

80  to  120. 

§ 

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140  exposed. 

Variegated  shale  and  clay, 
containing  sandstone  lay- 
ers, one  above  the  middle 
of  the  formation;  cinna- 
mon-brown color;  bone- 
bearing; limestone  layers 
sometimes  present  i n 

lower  part. 

Dove  - colored  limestone, 
overlain  by  reddish-brown, 
coarse-grained  sands  tope, 
coarsely  conglomeratic  at 
base. 

Sandstone,  red  and  green 
shales,  clays,  and  lime- 
stone, with  an  occasional 
bed  of  gypsum  in  lower 
part;  also  one  at  the  top. 

1 

Massive,  light -grav  lime- 
stone and  argillaceous 
shale. 

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24  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

SEDIMENTARY  ROCKS. 

CARBONIFEROUS  SYSTEM. 

MADISON  LIMESTONE. 

General  statement.— The  Madison  limestone  is  very  conspicuous 
along  the  north  side  of  the  Little  Belt  Mountains,  but  the  greater 
part  of  it  lies  outside  of  the  area  here  described.  The  only  exposures 
in  the  district  are  along  East  Fork  of  Sand  Coulee  and  its  tributaries 
and  on  Smith  River,  where  a local'  doming  of  the  beds  exposes  100 
to  200  feet  of  the  formation.  Its  distribution  is  shown  on  the  geologic 
map  (PL  I).  Along  the  flanks  of  the  Little  Belt  Mountains  outside 
of  the  area  to  which  this  report  relates  the  limestone  has  a thickness 
of  about  1,000  feet  and  consists  of  three  members.  The  lowest 
member,  which  is  more  or  less  argillaceous,  has  been  called  the 
Paine  shale,  the  more  massive  limestone  of  the  middle  part  the 
Woodhurst  limestone,  and  the  top  member  the  “ Castle”  limestone. 
In  the  Little  Belt  Mountains  the  Madison  limestone  carries  a typical 
Mississippian  fauna. 

“ Castle ” limestone  member. — The  “Castle”  limestone  member, 

which  forms  “Sluicebox  Canyon,”  the  lower  end  of  which  is  at 

Riceville  (PL  V),  is  exposed  to  view  at  numerous  places  in  the 

vicinity  of  Stockett;  farther  south,  in  the  head  of  Ming  Coulee; 

and  on  Smith  River.  Within  the  area  examined  its  greatest 

observed  thickness  is  about  140  feet,  which  is  found  at  the 

head  of  Ming  Coulee,  about  10  miles  southwest  of  Stockett.  Here 

the  rock  is  massive,  compact,  and  of  a medium-gray  color,  but 

weathers  light.  It  occurs  in  strata  15  to  20  feet  thick,  which  at 

many  places  have  weathered  to  rough,  cavernous  surfaces,  forming 

castellated  masses.  Interbedded  with  the  massive  strata  are  thin 

layers  of  softer  calcareous  material.  At  Stockett  15  feet  of  oolitic 

limestone  was  observed  in  this  formation,  underlain  by  compact 

light-colored  limestone.  The  fossils  listed  below  were  collected  from 
© 

the  limestone  at  Stockett  and  at  the  head  of  Ming  Coulee,  outside 
of  the  area  described: 

Fossils  from  Stockelt,  Mont. 

Spiriferina  solidirostris. 

Seminula  madisonensis. 

Seminula  liumilis. 

Cleiothyridina  crassicardinalis. 

Eumetria  verneuiliana. 

Fossils  from  head  of  Ming  Coulee. 

Schuchertella  sp.  Eumetria  verneuiliana. 

Spiriferina  solidirostris.  Camarotoechia  sp. 

Seminula  madisonensis. 


Amplexus  sp. 

Zaphrentis  sp. 
Syringopora  surcularia. 
Schucliertella  sp. 
Spirifer  centronatus  var. 


GEOLOGICAL  SURVEY 


MADISON  LIMESTONE  OVERLAIN  BV  QUADRANT  SHALE,  NEAR  RICEVILLE,  MONT, 


STRATIGRAPHY. 


25 


These  fossils  were  determined  by  George  H.  Girty,  who  regards 
them  as  Mississippian  in  age. 

The  Madison  limestone  in  the  vicinity  of  Riceville  is  overlain  by 
the  brick-red  sandy  shale  or  impure  sandstone  of  the  Quadrant 
formation,  but  farther  west,  in  Sand  Coulee  and  its  tributaries,  and 
also  at  the  head  of  Ming  Coulee  and  on  Smith  River,  the  Quadrant 
is  absent,  the  basal  limestone  or  the  calcareous  conglomeratic  sand- 
stone of  the  Ellis  formation  resting  upon  the  Madison  limestone. 
These  unconformable  relations  are  shown  in  cross  section  C-C,  PL  I, 
and  on  PL  VI. 


QUADRANT  FORMATION. 

Character  and  extent. — The  Quadrant  formation  comprises  a suc- 
cession of  beds  of  variable  character  and  thickness  which  immediately 
overlie  the  Madison  limestone  in  most  places  throughout  the  Little 
Belt  Mountains  region.  These  beds,  although  different  in  character, 
have  been  regarded  by  Weed  as  the  stratigraphic  equivalent  of  the 
Quadrant  formation  near  Quadrant  Mountain  in  the  Yellowstone 
Park  region,  where  the  name  was  first  applied.  The  Quadrant  for- 
mation in  the  Great  Falls  field  consists  of  sandy  shale  or  argillaceous 
sandstone  and  limestone  with  beds  of  gypsum  in  the  lower  part  and 
near  the  top.  It  is  not  coal  bearing,  and  consequently  is  not  included 
in  the  area  studied  except  at  a few  localities,  notably  on  Belt  Creek 
near  Riceville,  on  Little  Otter  Creek  2J  miles  above  its  mouth,  along 
the  base  of  Little  Belt  Mountains  from  Geyser  Creek  to  near  the 
southeast  corner  of  the  area  described,  and  in  the  central  part  of 
Skull  Butte.  No  careful  study  was  made  of  the  stratigraphy  of  the 
formation  except  on  Belt  Creek  near  Riceville,  where  the  basal  mem- 
ber consists  mainly  of  red  and  green  sandy  shale  with  an  occasional 
bed  of  white  gypsum  and  a few  thin  layers  of  white  limestone.  Very 
few  typical  sandstone  members  were  observed  at  this  locality, 
although  Weed  a has  applied  the  name  Kibbey  sandstone  to  the  basal 
member  of  the  Quadrant  in  this  general  region.  The  upper  member 
of  the  section,  which  the  same  writer  has  designated  the  Otter 
shale,  consists  largely  of  red  and  green  sandy  shale  with  limestone 
layers  occurring  at  frequent  intervals.  No  gypsum  was  observed  in 
this  part  of  the  section  except  near  the  top.  The  following  section 
of  a part  of  the  formation  was  measured  near  Riceville: 

Section  of  part  of  Quadrant  formation  on  east  side  of  Belt  Creek  near  Riceville , Mont. 

Ft.  in. 


Shale,  dark  green. . j. 51 

Limestone,  white 1 

Shale,  green,  sandy 1 


a Weed,  W.  H.,  Description  of  the  Fort  Benton  district:  Geologic  Altas  U.  S.,  folio  55,  U.  S.  Geol. 
Survey,  1899. 


26 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


Section  of  part  of  Quadrant  formation  on  east  side  of  Belt  Creek  near  Riceville , 

Continued. 


Ft. 

Limestone,  white,  compact,  laminated 2 

Shale,  dark  greenish 20 

Shale,  greenish,  sandy 20 

Limestone,  dove-colored,  thinly  laminated 1 

Shale,  red  and  green,  containing  hard  limestone  layers  68  inches 

thick 25 

Limestone,  alternating  layers  of,  and  shale,  greenish 7 

Shale,  red,  containing  layers  of  dove-colored  limestone  in  lower 

part 14 

Limestone,  blue,  compact,  porous 3 

Limestone  and  shale,  gray,  alternating  layers  of  white  and  dove- 
colored  limestone  thinly  laminated,  with  an  occasional  bed  of 

' gray  shale 20 

Soft  sandy  material 11 

Limestone,  hard,  gray,  compact 3 

Shale,  dark  green,  sandy 20 

Limestone,  hard,  gray,  compact 1 

Soft  sandy  material 8 

Gypsum,  white 3 

Gypsum,  impure,  and  dark-gray  shale,  with  nodules  of  black 

flint 6 

Shale,  greenish,  sandy,  containing  thin  layers  of  white  limestone. . 34 

Limestone,  white.. 

Shale,  green,  sandy , 6 

Limestone,  white 

Shale,  green,  sandy 29 

Limestone,  white,  compact 2 

Gypsum,  white 2 

Shales,  red  and  green,  sandy .* 34 

Beds  concealed 7 

Shale,  red 17 

Madison  limestone. 


Mont.- — 


in. 

6 


6 

6 

6 

6 


6 

8 


6 


Total 


352  2 


The  total  thickness  of  the  formation  as  observed  near  Riceville  is 
less  than  500  feet,  but  according  to  Weed®  its  thickness  greatly 
increases  toward  the  southeast,  reaching  a total  of  1,400  feet  near 
Utica.  Farther  east,  along  the  Little  Belt  and  Big  Snowy  mountains, 
W.  R.  Calvert  6 has  observed  that  the  Quadrant  has  a thickness  vary- 
ing from  450  to  750  feet,  while  its  lithologic  character  is  not  materially 
different  from  that  shown  on  Belt  Creek,  except  for  the  absence  of 
beds  of  gypsum. 

The  Quadrant  formation  is  overlain  unconformably  by  the  basal 
limestone  and  conglomeratic  sandstone  of  the  Ellis  formation,  and 
rests  with  apparent  conformity  on  the  underlying  Madison.  There 
is,  however,  a very  abrupt  change  in  the  character  of  the  rocks  at 

a Weed,  W.  H.,  Twentieth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3,  1898-99,  p.  295. 
b Calvert,  W.  R.,  Geology  of  the  Lewistown  coal  field,  with  special  reference  to  coal:  Bull.  U.  S* 
Geol.  Survey  (in  preparation). 


STRATIGRAPHY. 


27 


the  Quadrant-Madison  contact,  probably  indicating  a hiatus.  The 
details  of  distribution  of  this  formation  are  shown  in  PI.  I. 

^^_previous  workers  in  this  field  have  published  statements 
concerning  the  age  of  the  Quadrant  which  are  somewhat  at  variance, 
having  assigned  the  formation  to  both  the  “ Lower”  and  “ Upper  ’’  Car- 
boniferous. While,  as  previously  stated,  no  special  study  was  made 
of  the  Quadrant  formation  during  the  investigation  of  the  Great 
Falls  coal  field,  subsequent  observation  has  thrown  some  light  on  the 
age  of  these  beds.  Along  the  north  side  of  the  Little  Belt  Mountains, 
in  the  vicinity  of  Utica,  a few  miles  beyond  the  eastern  border  of  the 
Great  Falls  coal  field,  W.  R.  Calvert  and  the  writer  obtained  a large 
collection  of  fossils  from  the  Quadrant,  and  Calvert  made  additional 
collections  from  this  formation  farther  east  in  the  Judith  basin.a 
These  collections  have  all  been  studied  by  George  H.  Girty,  who 
makes  the  following  statements  concerning  their  age  : 

The  several  collections  made  in  the  Quadrant  in  this  area  indicate  a single  uniform 
fauna.  A definite  opinion  as  to  the  age  of  the  Quadrant  fauna  must  be  reserved  until 
more  complete  evidence  has  been  obtained  and  more  extensive  investigations  have 
been  undertaken,  for  the  facies  is  very  largely  new  to  the  American  Carboniferous. 
At  present  it  seem  probable  that  the  Quadrant  will  prove  to  be  of  early  Pennsylvanian 
or  Pottsville  age.  Faunas  which  have  an  upper  Mississippian  facies  and  are  younger 
than  the  Madison  have  been  cited  from  the  Little  Belt  Mountains  and  referred  to  the 
Quadrant.  They  are  considerably  different  from  the  Quadrant  fauna  of  this  report, 
and  it  seems  possible  that  three  distinct  faunas  will  be  involved  in  the  problem — a 
Madison  fauna,  a late  Mississippian  fauna,  and  a post-Mississippian  fauna.  The  fauna 
of  the  typical  Quadrant  is  at  present  unknown. 

JURASSIC  SYSTEM. 

ELLIS  FORMATION. 

Character  and  extent. — The  Ellis  formation  includes  a basal  lime- 
stone of  variable  thickness,  ranging  from  15  to  60  feet,  which  in  places 
merges  upward  into  a coarse  conglomerate  that  passes  into  a medium- 
grained sandstone,  light  brown  to  gray  in  color,  and  more  or  less  thin 
bedded.  In  other  localities,  however,  the  change  from  limestone  to 
conglomerate  is  abrupt.  The  limestone  and  conglomerate  contain 
marine  Jurassic  invertebrate  fossils.  Some  of  those  in  the  conglomer- 
ate are  fragmentary,  but  more  are  complete,  with  pebbles  of  lime- 
stone and  quartzite  several  inches  in  diameter.  The  component  parts 
of  the  conglomerate  are  bound  together  by  a calcareous  cement.  The 
total  thickness  of  the  formation  is  about  80  to  120  feet.  It  rests 
unconformably  upon  the  shale  of  the  Quadrant  formation  in  certain 
parts  of  the  field,  and  upon  the  Madison  limestone  in  others.  (PI.  VI. ) 

The  exposed  area  of  the  Ellis  formation  is  not  large  throughout  the 
Great  Falls  region.  It  is  exhibited  in  the  sides  of  the  bluffs  bordering 
Smith  River  and  its  tributary,  Hound  Creek,  also  along  Sand  Coulee 


a Op.  Cit. 


28  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

and  its  various  branches  in  the  vicinity  of  Stockett,  and  along  Belt 
Creek  from  Armington  to  the  southern  border  of  the  district.  East  of 
Belt  Creek  the  formation  is  exposed  in  the  head  of  Otter  Creek  and  its 
numerous  branches  from  the  south ; also  throughout  a zone  of  varying 
width  extending  to  the  southeast  along  the  northern  slope  of  the 
Little  Belt  Mountains.  Skull  Butte  is  encircled  by  a narrow  band  of 
the  formation.  The  details  of  distribution  of  the  Ellis  formation  are 
shown  on  the  geologic  map  (PI.  I). 

The  following  sections  illustrate  the  succession  of  the  beds  of  the 
formation  in  different  parts  of  the  field : 

Section  of  Ellis  formation  near  Goodman  siding , Montana. 

Feet. 

Sandstone,  massive,  light  brown  to  gray,  weathering  tan,  conglomer- 


atic and  fossiliferous  at  base 66 

Limestone,  reddish  brown,  fossiliferous 6 

Beds  concealed  (estimated) 18 


90 

Section  of  Ellis  formation  at  head  of  Ming  Coulee , Montana. 

Feet. 


Sandstone,  gray,  weathering  brown,  thin  bedded 60 

Sandstone,  gray,  conglomeratic,  containing  marine  Jurassic  fossils  . . 29 

Limestone,  dove  colored,  massive;  basal  member  brecciated  and 
containing  Jurassic  fossils 60 


149 

Fossils. — Fossil  invertebrates,  mainly  Ostrea  and  Camptonectes , are 
present  in  great  abundance  in  the  two  lower  members  of  the  above 
section.  The  numerous  specimens  of  these  genera  and  a few  other 
forms  are  sufficient  to  determine  that  the  rocks  belong  to  the  Ellis  for- 
mation, which  in  the  Yellowstone  National  Park  and  neighboring 
areas  yields  a characteristic  upper  Jurassic  fauna.  The  sandstone  of 
the  Ellis  formation  throughout  the  Great  Falls  region  is  usually  not 
fossiliferous,  but  the  conglomerate  and  underlying  limestone  contain 
an  abundance  of  Jurassic  fossils.  Near  the  head  of  Hazlett  Creek,  in 
sec.  31,  T.  16  N.,  R.  11  E.,  forms  were  collected  from  thin  layers  of 
limestone  near  the  base  of  the  Ellis  formation,  and  were  identified  by 
T.  W.  Stanton  as  Rliynchonella  myrina  Meek?,  Ostrea  strigilecula 
White,  Camptonectes  sp.,  and  Belemnites  sp. 

From  the  conglomerate  sandstone  of  the  Ellis  formation  on  the  east 
side  of  Otter  Creek  a small  collection  of  fossils  was  made,  from  which 
T.  W.  Stanton  recognized  a smooth,  simple  form  of  Ostrea , very  abun- 
dant; Ostrea  ( Alectryonia ) sp.;  and  Eumicrotis  curta  Hall?. 

MORRISON  SHALE  (?). 

Character  and  extent. — The  Morrison  formation,  which  is  extensively 
exposed  along  the  Rocky  Mountain  front  range  in  southern  Montana 


BULLETIN  NO.  356  PL. 


BASAL  JURASSIC  SANDSTONE  LYING  UNCONFORMABLY  ON  MADISON  LIMESTONE  NEAR  STOCKETT,  MONT. 

A is  about  1 mile  south  of  B. 


STRATIGRAPHY. 


29 


and  Wyoming,  is  also  believed  to  occur  along  the  northern  base  of  the 
Little  Belt  Mountains.  In  previous  investigations  in  this  field  by 
Weed  and  others  the  Morrison  formation  has  not  been  recognized,  and 
the  beds  comprising  it  have  been  grouped  with  the  Kootenai  and 
included  in  the  “ Cascade  ” formation.  During  the  last  field  season  dino- 
saur bones  provisionally  regarded  by  C.  W.  Gilmore  as  of  Jurassic  age 
were  found  at  one  horizon  in  many  different  localities;  and  at  one 
exposure  in  sec.  3,  T.  16  N.,  R.  2 E.,  about  30  feet  below  the  bone- 
bearing bed,  a green  shale  containing  a distinctly  fresh- water  fauna 
later  than  the  Ellis  formation  was  seen.  These  rocks,  here  provision- 
ally regarded  as  constituting  the  Morrison  formation,  consist  of  sand- 
stone and  bright-colored  sandy  shale  with  scattered  layers  of  impure 
-limestone,  many  of  them  in  lenticular  form.  The  formation  lies  with 
apparent  conformity  on  the  Ellis  and  is  overlain  conformably  by  the 
Kootenai.  The  thickness  ranges  from  60  to  120  feet,  but  the  exact 
limits  of  the  formation  are  in  many  places  difficult  to  determine. 
Fragments  of  bone  have  been  found  at  different  horizons  throughout 
the  overlying  Kootenai  formation,  but  thus  far  none  that  are  suffi- 
ciently well  preserved  for  specific  determination  have  been  discovered  in 
this  region.  It  is  possible  that  future  investigation  may  prove  that 
the  rocks  here  tentatively  regarded  as  belonging  to  the  Morrison  con- 
stitute in  reality  a basal  member  of  the  Kootenai. 

The  formation  is  generally  exposed  in  a narrow  band  on  the  inner 
rim  of  a low  ridge  formed  by  the  harder  overlying  rocks  of  the  Koote- 
nai formation.  It  outcrops  all  along  the  base  of  the  Little  Belt  Moun- 
tains, from  the  east  end  of  the  district  to  Smith  River.  Good  expo- 
sures occur  along  the  upper  courses  of  Sage,  Skull,  Running  Wolf, 
Hazlett,  Surprise,  Geyser,  and  Otter  creeks  and  in  the  bluffs  for  some 
distance  back  from  the  mountains  along  Belt  Creek,  Sand  Coulee, 
Smith  River  and  its  principal  tributar}r,  Ming  Coulee.  The  following 
sections  show  the  succession  of  the  beds: 

Section  of  supposed  Morrison  formation  on  the  north  side  of  Smith  River  in  the  /SIP.  \ sec. 

29,  T.  17  N.,  R.  3 E.,  Montana. 


Kootenai  formation. 

Morrison  formation : Feet 

Shale,  soft,  sandy 52 

•Limestone,  light-colored,  nodular 4 

Shale,  variegated 33 

Sandstone,  gray,  massive 11 

Shale,  greenish  gray,  sandy 20 

Ellis  formation. 


120 


30  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

Section  of  supposed  Morrison  formation  on  the  east  side  of  Belt  Creek  in  the  NE.  \ sec.  30, 


T.  18  N.,  R.  7 E.,  Montana. 

Kootenai  formation. 

Morrison  formation : Feet. 

Shales,  maroon  and  green 52 

Shale,  green,  capped  by  \\  feet  of  sandstone,  gray 5 

Sandstone,  calcareous,  weathering  light  brown 5 

Shale,  greenish 20 

Sandstone,  massive,  weathering  light  brown 7 

Shale,  dark  green,  containing  thin  limestone  layers 9 

Ellis  formation. 

98 


Section  of  Morrison  and  part  of  Kootenai  formation  in  the  NE.  ^ sec.  3,  T.  16  N.,  R.  10  E., 


near  Shannon  Creek , Montana. 

Kootenai  formation : Ft.  in. 

Sandstone,  gray,  massive 60 

Coal  (estimated) 6 

Beds  concealed 60 

Morrison  formation : 

Beds,  concealed 22 

Shales,  red  and  green,  containing  ironstone  layers  at  base 46 

Limestone,  light  colored,  fossiliferous 5 

Shale,  green,  sandy,  fossiliferous 25 

Limestone,  white,  fine-grained,  thin  bedded 6 

Shale,  green,  sandy ' 13  ■ 


237  6 

Fossils. — Invertebrate  fossils  collected  from  a locality  where  Shannon 
Creek  was  measured  have  been  examined  by  T.  W.  Stanton,  who 
reports  three  species  of  Unio,  apparently  all  undescribed;  Neritina  sp. 
and  Valvata  cf.  scabrida  M.  and  H.  Mr.  Stanton’s  comments  on  this 
collection  are  as  follows : 

This  is  a fresh-water  fauna  later  than  the  Ellis  and  suggestive  of  the  Morrison, 
although  there  are  no  identical  species,  with  the  possible  exception  of  the  Valvata. 

From  the  red  and  green  shales  about  1 mile  west  of  the  above- 
described  locality  were  collected  saurian  bones  which  C.  W.  Gilmore 
describes  as  “a  portion  of  the  centrum  of  a large  vertebra,  which, 
from  its  size,  might  well  represent  one  of  the  large  herbivorous 
dinosaurs  of  the  Jurassic  (Morrison).” 

CRETACEOUS  SYSTEM. 

KOOTENAI  FORMATION. 


General  statement. — The  Kootenai  formation,  as  determined  by  the 
present  investigation,  comprises  the  upper  one-third  of  the  Cascade 
and  Dakota  and  the  basal  red  shale  included  in  the  Colorado  shale, 
as  described  by  Weeda  in  the  Fort  Benton  folio.  The  name  Cascade, 


a Weed,  W.  H.,  Geologic  Atlas  U.  S.,  folio  55,  U.  S.  Geol.  Survey,  1899, 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  356  PL.  VII 


Formations. 


Character  of  Rocks. 


Shales,  dark,  with  layers  of  sandstone. 


Beds  partly  concealed;  thin-bedded  sandstone  at  base. 


Beds  concealed 

Sandstone,  dark  gray,  soft 

Sandstone,  dark  gray,  hard,  forming  bold  ledge 

Colorado 

(Upper  Cretaceous)  Sandstone,  gray 


Shales,  dark  gray,  sandy 


Shales,  greenish,  sandy. 


Shales,  red,  sandy,  only  partly  exposed 


Kootenai 

(Lower  Cretaceous) 


Shales,  reddish,  sandy,  with  thin-bedded  sandstone. 

Limestone,  light  brown,  compact,  fossiliferous 

Shale,  purplish,  with  lilac  thin-bedded  sandstone  . . . 
Shales,  light,  sandy,  capped  by  sandstone 


Shales,  purplish,  with  limestone  and  sandstone 

Clay,  red,  capped  by  sandstone 

Conglomerate,  clay -ball,  capped  by  rust-colored  limestone. 
Shales,  greenish  to  purple,  sandy,  with  limestone  lenses  .- . 


Sandstone,  gray,  massive,  shaly  at  base 

Shales,  dark  gray 

Coal. 


Shales,  greenish,  soft,  sandy. 


Morrison 
(Cretaceous  or 
Jurassic) 


Sandstone,  gray,  massive,  thin  bedded  at  base 

Conglomerate,  pebbly,  lenticular 

Shales,  maroon  and  greenish,  sandy 

Shales,  sandy,  and  calcareous  sandstone .1 

Shales,  green,  sandy I 

Sandstone,  tan-colored,  massive [ 

Shale,  dark  green,  containing  layers  of  limestone ’ 


Ellis 

(Jurassic) 


Sandstone,  gray,  massive,  conglomeratic,  fossiliferous 


Limestone,  conglomeratic,  fossiliferous 

Shales,  dark  green,  with  beds  of  clay  at  top 

Gypsum 


Shales,  variegated,  sandy,  alternating  with  limestone. 


Quadrant 

(Pennsylvanian) 


Madison 

(Mississippian) 


Shales,  dark,  with  limestones  at  base 

Limestones,  white  and  dove-colored . . . . . . . . . . . . 

Shale,  sand,  and  hard,  brecciated  limestone 

Shale,  dark  green [ 

Gypsum,  lenticular 

Shales,  green,  sandy,  with  thin  white  limestone  at  base 

Shales,  green,  sandy,  alternating  with  white  limestone. . . 

Gypsum 

Shales,  red  and  green,  soft,  sandy 

Shale,  red,  sandy 

Limestone,  white,  massive 


300  feet 


COLUMNAR  SECTIONS  SHOWING  STRATIGRAPHY  IN  DIFFERENT  PARTS  OF  GREAT  FALLS  REGION,  MONTANA. 


. 


•'  ; . , 


STRATIGRAPHY. 


31 


as  referred  to  a Cretaceous  formation,  was  first  used  by  that  author  in 
his  description  of  the  rocks  of  the  Fort  Benton  quadrangle,  to  apply 
to  a series  of  beds  ranging  in  thickness  from  225  to  500  feet.  The  lower 
part  of  the  formation,  as  originally  described,  consisted  of  lavender- 
tinted  sandstone  containing  at  its  base  a workable  bed  of  coal.  Dur- 
ing the  present  investigation,  as  previously  stated,  saurian  bones 
believed  by  C.  W.  Gilmore,  of  the  United  States  National  Museum,  to 
be  of  Jurassic  age,  were  discovered  in  the  lower  half  of  the  so-called 
“ Cascade  ” formation,  indicating  that  these  beds  are  probably  of  Morri- 
son age,  although  vertebrate  remains  occur  in  the  sandstones  of  the 
overlying  Kootenai.  Between  a horizon  45  feet  below  the  coal  bed 
and  the  top  of  the  “ Cascade”  formation  as  above  defined  fossil  plants 
of  Kootenai  age  were  collected  at  five  different  horizons,  establishing 
beyond  question  the  Lower  Cretaceous  age  of  this  portion  of  the  forma- 
tion. On  the  east  side  of  Spanish  Coulee,  a tributary  of  Smith  River, 
at  a horizon  about  150  feet  above  the  “ Cascade’ ’ formation,  in  beds 
the  equivalent  of  which  in  the  vicinity  of  Belt  have  been  provisionally 
regarded  by  Weed  as  of  Dakota  age,  a large  collection  of  Kootenai 
plants  was  procured  from  dark-colored  shale  associated  with  red  and 
green  shales  and  clay.  Overlying  this  plant-bearing  bed  is  about  200 
feet  of  rocks  consisting  of  red  shale  and  sandstone  not  differing  mate- 
rially in  stratigraphy  or  lithologic  character  from  beds  immediately 
underlying  the  plant  horizon.  The  close  lithologic  resemblance  of 
this  upper  member  to  the  underhung  well-defined  Kootenai  rocks, 
together  with  the  apparent  absence  of  Dakota  floras  in  it,  has  been 
regarded  by  the  writer  as  sufficient  evidence  for  provisionally  includ- 
ing the  beds  in  question  as  of  Kootenai  or  Lower  Cretaceous  age.  These 
beds  are  overlain  by  dark-colored  shale  and  sandstone  of  the  Colorado 
formation,  in  the  lower  part  of  which  were  discovered  marine  saurian 
remains. 

In  this  report  it  does  not  seem  advisable  to  employ  the  name 
“Cascade”  for  the  following  reasons:  First,  the  term  has  not  been  so 
extensively  used  in  the  literature  as  the  term  Kootenai;  second,  its 
usage  would  necessitate  redefining  the  term,  in  order  to  separate  its 
lowest  member,  which  is  now  believed  to  be  Morrison:  third,  the  beds 
immediately  overlying  the  “Cascade”  formation  can  not  be  differen- 
tiated paleontologically  from  it,  both  being  of  Lower  Cretaceous  age, 
rendering  it  necessary  to  place  the  upper  limit  of  the  formation  in 
question  purely  on  lithologic  grounds. 

Character  and  extent. — The  Kootenai  formation  consists  of  alter- 
nating layers  of  sandstone  and  shale,  with  the  former  predominating, 
especially  in  the  lower  half.  The  sandstones  range  in  thickness 
from  10  to  60  feet,  and  are  more  or  less  massive  in  character.  In 
the  upper  part  shales  are  more  abundant  and  are  interbedded  with 
thin  layers  of  impure  sandstone.  At  Belt,  on  the  east  side  of  Belt 


32 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


Creek,  where  a complete  section  was  measured,  the  basal  member 
of  the  formation  consists  of  a sandy  shale  interbedded  with  sandstone, 
the  latter  predominating,  the  whole  having  a thickness  of  about 
60  feet.  This  member  consists  locally  of  firm,  massive  sandstone 
with  only  a small  percentage  of  shale.  It  is  overlain  by  coal,  which 
here  has  a thickness  of  6 feet,  including  a few  thin  partings.  Above 
the  coal  there  is  a dark,  coaly  shale  5 to  6 feet  thick,  covered  by  38 
feet  of  massive  light-gray  sandstone.  This  sandstone  is  overlain  by 
138  feet  of  beds,  consisting  in  ascending  order  mainly  of  alternating 
layers  of  sandstone,  red  shale,  and  clay,  with  an  occasional  limestone 
lens  in  the  lower  part.  Above  this  alternating  series  there  is  about 
200  feet  of  red  shale,  which  constitutes  the  topmost  member  of  the 
formation.  The  total  thickness  is  about  450  feet,  which  may  be 
regarded  as  representative  of  the  Kootenai  formation  as  exposed 
along  the  Belt  Creek  valley. 

In  previous  reports  on  the  geology  of  this  region  by  Weed  a greatly 
exaggerated  thickness  (736  feet)  was  assigned  to  beds  lying  between 
the  base  of  the  Ellis  and  the  coal  bed  of  the  Kootenai  formation.  Of 
this  amount  the  lower  215  feet  was  regarded  as  belonging  to  the 
Ellis  and  the  remainder  to  the  Kootenai  formation,  the  presence  of  the 
Morrison  between  these  two  formations  not  having  been  recognized. 
During  the  present  investigation  a number  of  detailed  sections 
measured  along  Belt  Creek  proved  conclusively  that  the  strati- 
graphic interval  between  the  base  of  the  Ellis  and  the  Kootenai  coal, 
to  which  Weed  had  assigned  a thickness  of  736  feet,  is  in  reality  only 
about  300  feet.  According  to  the  present  classification  the  lower 
120  feet  of  these  beds  has  been  assigned  to  the  Ellis;  an  equal  thick- 
ness immediately  overlying,  in  which  fresh-water  invertebrates  and 
land  animals  occur,  to  the  Morrison;  and  the  upper  60  feet,  which 
is  plant  bearing,  to  the  Kootenai.  PL  IV,  which  contains  a number 
of  columnar  sections  measured  along  Belt  Creek  valley,  illustrates 
the  character  and  thickness  of  the  various  formations. 

On  the  north  side  of  Skull  Butte  the  base  of  the  Kootenai  consists 
of  a soft  light-gray  massive  sandstone,  but  in  other  respects  the 
portion  of  the  formation  exposed  in  this  locality  agrees  closely  with 
the  beds  exhibited  at  Belt  Butte.  A section  of  the  Kootenai  on  the 
north  side  of  Skull  Butte  is  given  below: 

Section  of  a part  of  Kootenai  formation  on  north  side  of  Skull  Butte , Montana. 


Shale,  reddish,  sandy.  Ft.  in. 

Sandstone,  gray,  thin  bedded 1 6 

Shale,  reddish,  sandy,  with  layers  of  sandstone  in  lower  part. . . 21 

Sandstone,  greenish,  gray,  weathering  dark;  thin  bedded  above, 

clay-ball  conglomerate  below 4 

Shale,  reddish,  sandy,  with  layers  of  sandstone  in  lower  part ...  27 

Sandstone,  gray,  cross-bedded;  clay-ball  conglomerate  in  lower 
part 5 6 


STRATIGRAPHY. 


33 


Section  of  a part  of  Kootenai  for  motion  on  north  side  of  Slcull  Butte , Montana — Cont’d 


Ft.  in. 

Shale,  reddish,  sandy - - 30 

Sandstone,  soft,  thin  bedded 20 

Sandstone,  gray,  massive;  clay-ball  conglomerate 3 6 

Shale,  red,  sandy 38 

Sandstone,  gray,  massive;  clay-ball  conglomerate 5 

Shale,  red,  sandy 24 

Sandstone,  calcareous,  alternating  with  sandy  shale 20 

Sandstone,  light  and  dark  gray,  massive,  fine  grained 86 

Coal  (estimated) 6 

Sandstone,  gray,  massive,  soft 62 


353  6 

The  Kootenai  has  the  greatest  areal  distribution  of  all  the  forma- 
tions outcropping  within  the  area.  It  caps  the  surface  for  a great 
part  of  the  district  lying  between  Smith  River  and  Belt  Creek,  and 
is  the  surface  formation  of  the  high  plateaus  south  of  Otter  Creek. 
Beyond  Otter  Creek  it  is  exposed  as  a band  of  varying  width  which 
narrows  toward  the  east. 

Fossils. — The  Kootenai  formation  of  the  Great  Falls  district  car- 
ries an  abundant  fossil  flora  of  Lower  Cretaceous  age.  Fossil  plants 
of  Kootenai  age  were  first  discovered  in  the  Great  F alls  coal  field  in 
1889  by  J.  S.  Newberry.®  From  these  fossils,  which  consisted  of  only  a 
few  species,  it  was  possible  to  correlate  the  rocks  of  the  Great  Falls 
region  with  the  Kootenai  north  of  the  international  boundary  line, 
described  by  George  M.  Dawson.  In  1890,  during  the  construction 
of  the  Great  Northern  Railway  line  between  Helena  and  Great  Falls, 
Mont.,  a larger  collection  of  Kootenai  plants  was  made  from  a rail- 
road cut  near  the  flood  siding  on  the  Missouri;  these  were  reported 
on  by  Newberry  in  1891. b About  the  same  time  that  the  above 
collection  was  obtained  F.  H.  Knowlton  and  A.  C.  Peale  made  a 
small  collection  of  plants  from  the  same  railroad  cut,  and  the  follow- 
ing year  W.  H.  Weed  also  procured  plants  from  this  locality  which 
were  studied  and  described  by  W.  M.  Fontaine  in  1892. c In  1894-95 
Kootenai  plants  were  found  at  a number  of  localities  by  W.  H.  Weed 
and  L.  F.  Ward,  mainly  south  and  east  of  Geyser.  These  were  de- 
scribed by  W.  M.  Fontaine  in  Ward’s  second  paper  on  the  11  Status 
of  the  Mesozoic  floras  of  the  United  States.”  d 

During  the  present  investigation  fossil  plants,  all  of  which  were 
studied  and  reported  on  by  F.  II.  Knowlton,  were  collected  from  five 
different  horizons — 15,  60,  70,  150,  and  300  feet  above  the  base  of 
the  Kootenai  formation.  The  lowest  horizon  was  on  Hazlett  Creek, 
where  the  following  species  were  collected  from  a dark-colored  sandy 

“School  of  Mines  Quart.,  vol.  8,  July,  1887,  p.  329. 

*>  Ain.  Jour.  Sci.,  3d  ser.,  vol.  61,  1891,  pp.  191-201,  PI.  XIV. 
c Proc.  U.  S.  Nat.  Mus.,  vol.  15,  1892,  pp.  487-495,  Pis.  LXXXII-LXXXIV. 
rfMon.  U.  S.  Geol.  Survey,  vol.  48,  1905,  pp.  284-315,  Pis.  LXXI-LXXIII. 

54937— Bull.  356—09 3 


34 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


shale  45  feet  below  the  coal  horizon  and  15  to  20  feet  above  the  base 
of  the  formation : 

Cladophlebis  heterophylla  Fontaine. 

Thyrsopteris  elliptica  Fontaine. 

Zamites  articus  Goppert. 

Zamites  apertus  Newberry  (?). 

Fragmentary  plant  remains  were  observed  in  the  dark-colored 
clay  underlying  the  coal  at  a number  of  localities;  and  a few  small 
collections  were  made,  the  largest  being  from  the  Meredith  mine,  on 
the  east  side  of  a small  coulee  tributary  to  Geyser  Creek,  about  6 
miles  southwest  of  Geyser,  Mont.  The  following  were  obtained: 

Cladophlebis  heterophylla  Fontaine. 

Cladophlebis  constricta  Fontaine. 

Cladophlebis  fisheri  Knowlton. 

Thyrsopteris  elliptica  Fontaine. 

Acrostichopteris  fimbriata  Knowlton. 

Dryopteris?  kootaniensis  Knowlton. 

Adiantum  montanense  Knowlton. 

Oleandra  graminsefolia  Knowlton. 

Ginkgo  sibirica  Heer. 

Podozamites  lanceolatus  (L.  and  H.)  Schimper. 

Zamites  articus  Goppert. 

Nilsonia  schaumburgensis  (Dunker)  Natliorst. 

On  the  north  side  of  Skull  Butte,  the  following  fossil  plants  were 
obtained  from  a light-colored  impure  sandstone  about  150  feet  above 
the  base  of  the  formation  and  86  feet  above  the  coal : 

Cladophlebis  heterophylla  Fontaine. 

Cladophlebis  browniana  (Dunker)  Seward. 

Protorhipis  fisheri  Knowlton. 

Sequoia  reichenbachi  (Geinitz)  Heer. 

Coniferous  leaves? 

The  highest  horizon  in  the  Kootenai  formation  at  which  plants 
were  collected  was  on  the  east  side  of  Spanish  Coulee,  a small  tribu- 
tary of  Smith  River  in  sec.  11,  T.  17  N.,  R.  2 E.,  where  the  following 
were  secured  : 

Thyrsopteris  elliptica  Fontaine. 

Chiropteris  spatulata  Newberry. 

Sequoia  gracilis  Heer. 

Zamites  apertus  Newberry. 

One  mile  south  of  Flood  siding,  about  5 miles  southwest  of  Great 
Falls,  on  the  Great  Northern  Railway  between  Great  Falls  and 
Helena,  a collection  of  plants  was  made,  some  of  which  are  listed 
below: 

Dryopteris  montanensis  (Fontaine)  Knowlton. 

Sequoia  gracilis  Heer. 

Podozamites  nervosa?  Newberry. 

Pterophyllum  montanense  (Fontaine)  Knowlton. 


STRATIGRAPHY. 


35 


In  the  bluffs  of  Missouri  River,  near  the  Boston  and  Montana 
smelter,  a large  collection  of  Kootenai  plants  was  made  by  O.  C.  Mort- 
son.  In  this  collection  representatives  of  the  following  species  occur: 

Dryopteris  montanensis  (Fontaine)  Knowlton. 

Sequoia  gracilis  Heer. 

Sequoia  ambigua  Heer. 

On  the  south  side  of  Missouri  River,  opposite  the  Boston  and  Mon- 
tana smelter,  a specimen  of  Ginkgo  sibirica  was  observed  by  the 
writer,  but  was  not  collected. 

The  collection  of  fossil  plants  obtained  from  the  Kootenai  forma- 
tion in  the  Great  Falls  region  during  the  present  investigation  of  the 
coal  resources  of  the  district  is  not  large,  hut  it  is  of  unusual  interest 
in  that  it  contains  a number  of  species  before  unknown  in  the  Koo- 
tenai rocks  of  the  United  States,  although  present  in  the  Canadian 
beds  of  this  age;  it  contains  also  a species  of  the  genus  Protorhipis 
not  previously  found  in  North  America,  as  well  as  some  believed  to 
be  new  to  science. 

In  addition  to  the  plants,  some  fresh-water  invertebrates  were 
collected  from  the  upper  part  of  the  Kootenai  during  the  investiga- 
tion. A list  is  given  below: 

Unio  farri  Stanton? 

Unio  sp. 

Corbula  sp. 

Campeloma  liarfowtonensis  Stanton? 

Goniobasis  ortinanni  Stanton? 

Yiviparus?  sp. 

These  fossils  are  too  imperfect  for  positive  identification,  but  the 
species  with  which  they  are  compared  occur  a few  miles  south  of 
Harlowton,  Mont.,  in  beds  that  belong  to  either  the  Kootenai  or  the 
Morrison. 

The  following  bibliographic  list  contains  the  more  important 
paleobotanical  papers  published  on  the  Kootenai  formation: 

Dawson,  Sir  William,  On  the  Mesozoic  floras  of  the  Rocky  Mountain  region  of 
Canada:  Trans.  Royal  Soc.  Canada,  vol.  3,  sec.  4,  Pis.  I-IV,  pp.  1-22.  1885. 

The  name  “Kootanie  series"  is  first  given  and  defined  in  this  paper,  p.  2. 

Newberry,  J.  S..  The  Great  Falls  coal  field,  Montana:  School  of  Mines  Quart., 
vol.  8,  pp.  327-330.  ^1887. 

Dawson,  Sir  William,  Cretaceous  floras  of  the  Northwest  Territories  of  Canada: 
Am.  Naturalist,  vol.  22,  pp.  953-959.  1888. 

Newberry,  J.  S.,  Flora  of  the  Great  Falls  coal  field,  Montana:  Am.  Jour.  Sci.. 
3d  ser.,  vol.  61,  PI.  XIV,  pp.  191-201.  1891. 

Dawson,  Sir  William,  Correlation  of  early  Cretaceous  floras  in  Canada  and  the 
United  States:  Trans.  Royal  Soc.  Canada,  vol.  10,  sec.  4,  figs,  (in  text)  1-16,  pp. 
79-93.  1892. 

Fontaine,  W.  M.,  Description  of  some  fossil  plants  from  the  Great  Falls  coal  field 
of  Montana:  Proc.  U.  S.  Nat.  Mus.,  vol.  15,  Pis.  LXXXII-LXXXIV,  pp.  487-495. 
1892. 


36  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

Ward,  L.  F.,,  and  Fontaine,  W.  M.,  Flora  of  the  Kootanie  formation:  Mon.  U.  S- 
Geol.  Survey,  vol.  48,  Pis.  LXXI-LXXIII,  pp.  277-315.  1905. 

Fontaine,  W.  M.,  Notes  on  some  Lower  Cretaceous  (Kootanie)  plants  from  Mon- 
tana: Mon.  U.  S.  Geol.  Survey,  vol.  48,  Pis.  LXXI-LXXIII,  pp.  284-315.  1905. 

Knowlton,  F.  H.,  Description  of  a collection  of  Kootenai  plants  from  the  Great 
Falls  coal  field  of  Montana:  Smithsonian  Misc.  Coll.,  vol.  50,  pt.  1,  pp.  105-128, 
Pis.  XI-XIV.  1907. 

COLORADO  SHALE. 

General  statement. — The  rocks  overlying  the  Kootenai  formation 
in  this  district  consist  mainly  of  dark-colored  shale  with  a number 
of  prominent  sandstone  members  in  the  lower  part.  This  shale  and 
sandstone  constitute  the  well-known  Fort  Benton  formation  of  the 
Meek  and  Hayden  upper  Missouri  River  section,  the  name  being 
derived  from  the  town  of  Fort  Benton,  on  Missouri  River,  about  40 
miles  below  Great  Falls.  The  exposures  on  which  the  original 
descriptions  were  based  and  by  which  the  stratigraphic  limits  of 
the  formation  were  determined  lie  far  to  the  east  in  Nebraska.  In 
northeastern  Nebraska,  along  Missouri  River,  throughout  the  Black 
Hills,  and  along  the  Rocky  Mountain  front,  the  Benton  formation  is 
usually  underlain  by  Dakota  sandstone  and  overlain  by  Niobrara 
limestone.  In  the  present  investigation  no  evidence  was  found  of 
the  presence  of  Dakota  sandstone  as  a separate  formation  in  the 
Great  Falls  field,  nor  is  the  formation  here  overlain  by  Niobrara 
limestone.  It  is  possible  that  in  this  region  the  Niobrara  is  repre- 
sented by  dark  shale,  as  Stanton  has  suggested,®  and  there  is  some 
paleontologic  evidence  in  support  of  this  belief.  If  the  upper  mem- 
bers of  the  shale  and  sandstone  series  do  represent  deposition  during 
Niobrara  time,  they  can  not  be  separated  stratigraphically  from  the 
underlving  Benton.  For  this  reason  the  rocks  which  lie  between  the 
top  of  the  Kootenai  and  the  base  of  the  Eagle  sandstone  are  de- 
scribed as  the  Colorado  shale.  This  name  was  used  in  the  same 
sense  by  Weed  in  the  Fort  Benton  folio. 

Character  and  extent. — The  Colorado  shale  is  well  developed  in 
this  general  region,  being  represented  by  about  1,600  feet  of  beds. 
The  entire  formation  does  not  occur  within  the  area,  but  only  the 
lower  three-fourths,  the  upper  members  being  exposed  to  the  north 
in  the  higher  portions  of  the  Highwood  Mountains.  In  the  vicinity 
of  Fort  Benton,  only  a few  miles  to  the  northeast,  the  Colorado  is 
essentially  a shale  formation  with  very  thin  beds  of  impure  sandstone- 
The  Mowry  shale  member,  which  constitutes  a conspicuous  division 
of  the  formation  to  the  southeast  along  the  Rocky  Mountain  front,  is 
present  here,  but  is  not  conspicuous,  owing  to  the  flat  dips  which 
prevail  throughout  the  area.  Along  the  south  side  of  the  Highwood 

a Geology  of  Yellowstone  National  Park:  Mon.  U.  S.  Geol.  Survey,  vol.  32, 1899,  p.  605.  Geology  and 
paleontology  of  the  Judith  River  beds:  Bull.  U.  S.  Geol.  Survey,  No.  257,  1905,  p.  11. 


STRATIGRAPHY. 


37 


Mountains  and  in  Belt  Butte  the  formation  contains  a bed  of  volcanic 
ash.  The  rock  is  pale  yellowish  gray,  weathering  white.  It  resem- 
bles porcelain  and  is  overlain  by  rock  of  similar  character  and  appear- 
ance. Samples  of  this  rock  were  collected  from  Belt  Butte  and 
from  a*locality  about  8 miles  northeast  of  Stanford.  Thin  sections 
have  been  examined  by  Albert  Johannsen,  who  describes  the  first  as 
follows:  ‘‘Cryptocrystalline  in  texture.  It  is  very  slightly  aniso- 
tropic, as  a de vitrified  glass  might  be.  There  are  a few  irregular 
anisotropic  patches  which  are  too  small  to  be  determined.  There 
is  also  a little  brownish  decomposed  material.  It  may  be  an  indu- 
rated volcanic  tuff  or  rhyolitic  glass.77  The  second  is  described  as 
“a  very  fine  grained,  compact  glass,  consisting  almost  entirely  of 
angular  fragments  very  slightly  devitrified,  and  a very  fewr  small, 
irregular  grains,  apparently  of  quartz,  but  too  small  to  be  determined. 
The  rock  is  very  homogeneous  and  uniform  in  appearance  throughout 
the  section.77 

The  presence  of  a bed  of  volcanic  ash  in  the  Colorado  shale  is  a 
local  feature,  for  it  is  absent  in  the  western  part  of  the  field. 

Southwest  of  Great  Falls,  where  the  Colorado  is  well  developed, 
its  basal  member  consists  of  a soft  massive  sandstone,  somewhat 
concretionary,  about  30  feet  thick.  Above  this  sandstone  is  approx- 
imately 35  feet  of  rocks  composed  largely  of  dark-colored  shale  with 
a fewr  sandstone  beds.  This  shale  is  overlain  by  gray,  coarse-grained, 
massive  sandstone  containing  concretionary  layers  and  an  occasional 
thin  bed  of  soft  sandy  shale,  the  whole  having  a thickness  of  about 
80  feet.  Above  the  sandstone  for  300  feet  the  beds  consist  mainly  of 
alternating  layers  of  sandstone  and  shale.  These  are  followed  by 
700  feet  of  beds  composed  of  uniformly  dark-colored  sandy  shale, 
which  constitutes  the  uppermost  member  of  the  Colorado  as  exposed 
in  this  field.  A good  exposure  of  the  lower  half  of  the  formation  is 
found  in  Belt  Butte,  where  the  beds  consist  of  alternating  layers  of 
massive  gray  sandstone  and  dark-colored  shale  with  the  volcanic  ash 
member  mentioned  above  present.  A section  of  the  beds  as  exposed 
on  the  west  side  of  Belt  Butte  follows : 


Section  of  Colorado  shale  in  Belt  Butte , Montana. 

Feet. 

Shale,  dark  gray,  sandy,  with  thin  layers  of  sandstone 80 

Sandstone,  dark  gray 10 

Volcanic  ash 30 

Shale,  dark  colored,  sandy,  with  thin  layers  of  sandstone 80 

Shale,  sandy;  or  impure  sandstone 20 

Shale,  dark,  sandy 75 

Sandstone,  gray;  forming  belt  around  Belt  Butte 50 

Shale,  dark,  sandy  in  lower  part 125 

Shale,  dark,  sandy;  containing  massive  sandstone  members;  locally 

calcareous  at  top 180 

Kootenai  formation.  


650 


88  GEOLOGY  OF  GREAT  S' ALLS  COAL  FTELD,  MONTANA. 

I'he  Colorado  shale  is  exposed  in  a wide  area  extending  along  the 
south  side  of  the  Highwood  Mountains  from  Belt  Creek  southeastward 
to  the  east  border  of  the  district,  although  much  of  the  area,  especially 
the  eastern  half,  is  covered  by  terrace  gravel.  Its  basal  sandstone 
members  occupy  the  summits  of  Red  Butte  and  continue  westward 
as  a plateau  capping  to  the  Missouri  River  valley.  Smith  River 
and  its  tributary  Goodwin  Coulee  cut  the  basal  sandstone  of  the  Colo- 
rado, exposing  the  underlying  Kootenai  rocks.  The  Colorado  shale 
occupies  the  surface  of  the  highland  lying  between  Missouri  and  Sun 
rivers,  also  north  of  these  streams  across  the  northern  border  of  the 
district.  Its  areal  distribution  is  about  equal  in  extent  to  that  of 
the  Kootenai,  as  is  shown  bj^  the  geological  map  (PI.  I). 

Fossils. — Invertebrate  fossils  were  found  in  the  Colorado  shale  at 
several  localities,  notably  near  Geyser,  where  collections  were  made 
at  four  different  localities  at  a point  1J  miles  northwest  of  Geyser, 
Inoceramus  labiatus  Schloth.  (?)  and  fragments  of  an  unidentified 
Inoceramus  were  obtained.  A mile  farther  northwest  the  following 

o 

were  collected : 

Inoceramus — large,  probably  unde-  Nucula  sp. 

scribed  species.  Cardium  sp. 

Leda  sp.  Prionotropis  sp. 

These  fossils  have  been  examined  by  T.  W.  Stanton,  who  regards 
them  of  Benton  age.  The  fossils  from  the  last-named  locality  are 
believed  to  represent  the  upper  part  of  the  Colorado  shale.  A few 
fragmentary  specimens  of  Inoceramus  were  found  on  the  west  side 
of  Belt  Butte,  on  the  south  side  of  Stanford  Buttes,  and  7 miles 
northeast  of  Stanford,  Mont.  The  fossils  were  collected  in  all  these 
places  at  a horizon  a few  feet  below  the  bed  of  volcanic  ash  above 
referred  to.  At  the  north  end  of  Square  Butte,  which  lies  about  2 
miles  west  of  the  area  here  discussed,  fossils  were  collected  at  a horizon 
believed  to  be  near  the  top  of  the  Colorado.  These  were  Ostrea  sp., 
possibly  Gryphsea,  and  fragments  of  Scaphites  ventricosus  M.  and  H. 
Fragmentary  remains  of  a swimming  saurian,  believed  by  C.  W. 
Gilmore  to  be  a plesiosaur,  were  collected  from  a bluish  shale  under- 
lying a prominent  sandstone  member  of  basal  Colorado  on  the  west 
side  of  Spanish  Coulee,  in  sec.  10,  T.  17  N.,  R.  2 E. 

The  Colorado  shale  rests  wdtli  apparent  conformity  upon  the 
underlying  Kootenai,  and  is  overlain  conformably  by  the  Eagle 
sandstone,  the  lowest  member  of  the  Montana  group.  Although 
conformable  relations  appear  to  exist  between  the  Kootenai  and 
Colorado  formations  in  this  region,  the  Dakota,  which  occupies  a 
position  between  these  two  formations  in  other  localities,  is,  as  pre- 
viously stated,  believed  not  to  be  present.  If  this  is  true,  there  is  a 
hiatus  at  this  contact  representing  at  least  several  hundred  feet  of 
beds.  It  is  possible  that  Dakota  time  is  here  represented  by 
marine  sediments  not  easily  separable  from  the  Colorado  shale. 


STRATIGRAPHY. 


39 


TERTIARY  AND  QUATERNARY  SYSTEMS. 

TERRACE  GRAVEL. 

General  statement. — Throughout  a great  part  of  the  territory  lying 
east  of  the  Otter  Creek  divide  the  plateaus  of  different  levels  which 
occupy  the  interstream  spaces  are  covered  by  gravel ; and  the  inter- 
mediate slopes,  especially  those  of  gentle  inclination,  are  in  many 
places  strewn  with  material  which  has  worked  down  from  the  higher 
terraces.  A few  isolated  areas  of  terrace  deposits  are  found  west 
of  thft  divide,  notably  those  between  Williams  and  Otter  creeks,  on 
either  side  of  Belt  Creek  below  the  town  of  Belt,  and  on  the  south 
side  of  the  Missouri,  below  the  mouth  of  Smith  River.  Smaller  areas 
lie  along  the  sides  of  the  creeks  and  at  low  levels  in  some  of  the  larger 
valleys,  especially  Belt  Creek.  These  are  generally  too  small  to  be 
shown  on  the  geologic  map.  To  the  northwest  are  terraces  believed 
to  be  contemporaneous  in  age  with  those  of  the  Great  Falls  field, 
reaching  far  out  on  the  plains  east  of  the  Levis  Range,  but  these  do 
not  extend  into  the  area  covered  by  this  report. 

Character. — The  terrace  gravel  is  diversified  in  character,  depend- 
ing on  its  location  relative  to  the  different  portions  of  the  adjoining 
mountains  whence  it  was  derived.  Those  deposits  which  occur  op- 
posite the  higher  portions  of  the  Little  Belt  Mountains,  where  crys- 
talline rocks  are  exposed,  contain  a relatively  high  percentage  of 
igneous  rock,  but  to  the  east,  where  sediments  from  the  crest  of  the 
mountains  and  crystalline  rocks  have  not  been  uncovered,  the  amount 
of  igneous  material  in  the  gravel  is  small.  The  deposits  in  general 
consist  of  sand  and  gravel  with  local  beds  of  clay.  The  component 
parts  of  the  gravel  are  of  varying  size,  ranging  from  that  of  a pea  to 
10  inches  in  diameter.  In  the  area  bordering  the  mountains  there  are 
some  bowlders  exceeding  a foot  in  diameter.  The  pebbles  are  rounded 
to  subangular,  and  none  were  seen  which  contained  striations. 

Mode  of  occurrence. — Terrace  deposits  of  three  distinct  levels  are 
found  in  the  eastern  part  of  the  Great  Falls  region.  The  highest  has 
been  definitely  recognized  at  only  one  locality — on  the  summit  of 
Stanford  Butte.  This  deposit,  which  has  been  described  by  Weeda 
as  the  Stanford  conglomerate,  consists  of  medium  to  large  sized  peb- 
bles, not  well  assorted,  cemented  into  a firm  conglomerate.  Rem- 
nants of  this  or  possibly  of  some  higher  terrace  gravel  are  found  on 
some  of  the  prominent  points  in  the  hilly  zone  bordering  the  Little 
Belt  Mountains,  but  the  correlation  of  the  material  of  these  localities 
with  that  of  Stanford  Butte  is  by  no  means  certain. 

The  second  terrace  is  about  100  feet  below  the  level  of  the  Stanford 
conglomerate,  and  carries  one  of  the  most  extensive  terrace  deposits 
of  the  district.  It  occupies  the  high  ridge  east  of  Skull  Creek,  along 


Weed,  W.  II.,  Geologic  Atlas  U.  S.,  folio  55,  U.  S.  Geol.  Survey,  1899. 


40  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

either  side  of  Surprise  Creek,  in  the  vicinity  of  Stanford  Butte,  and 
extends  far  to  the  east  as  a prominent  topographic  feature  on  either 
side  of  Arrow  Creek. 

The  third  and  lowest  terrace  covers  the  broad  flat  of  Running  Wolf 
Creek  valley  east  of  Stanford,  and  is  also  found  at  low  levels  on  Geyser 
Creek  and  its  principal  tributaries.  East  of  Stanford  this  terrace  is 
only  a few  feet  above  the  flood  plain  of  the  present  valley.  The  thick- 
ness of  the  deposit  ranges  from  5 to  35  feet  in  different  parts  of  the 
field.  It  lies  along  either  side  of  the  streams,  and  has  smooth  sur- 
faces which  slope  gently  away  from  the  mountains  toward  the  plains. 

Origin  of  terraces. — It  is  apparent  from  a study  of  the  composition 
of  the  gravel  deposits  that  their  source  was  mainly  in  the  Little  Belt 
Mountains  to  the  southwest,  but  little  definite  evidence  could  be  ob- 
tained as  to  the  manner  in  which  they  were  laid  down.  It  is  believed 
that  the  gravels  were  brought  down  by  streams  from  the  Little  Belt 
Mountains,  and  spread  by  them  over  the  lower  plains  country,  as 
their  courses  were  shifted  from  time  to  time,  but  it  seems  probable 
that  the  cause  which  resulted  in  the  development  of  the  different 
terrace  levels  was  not  normal  to  the  streams  of  that  period,  but  was 
accidental.  Whether  the  terraces  resulted  from  uplift  in  the  region, 
with  subsequent  rejuvenation  of  the  streams,  or  from  changes  in  cli- 
matic conditions  is  difficult  to  determine.  The  latter  seems  more 
probable,  especially  in  the  case  of  the  more  recent  terraces,  which 
were  probably  formed  during  Pleistocene  time.  No  definite  evidence 
could  be  found  to  show  that  the  older  terraces  were  not  formed  by 
uplift. 

Age. — The  age  of  the  different  gravel  terraces  in  the  Great  Falls 
field  can  not  be  definitely  stated.  The  two  higher  terraces  are  post- 
Miocene  to  early  Quaternary  in  age ; the  third  and  smaller  subsequent 
terraces  date  from  the  occupation  of  this  area  by  the  Keewatin  ice 
sheet,  in  Wisconsin  time,  nearly  to  the  present  day. 

The  conclusion  regarding  the  age  of  the  earlier  terraces  is  based  on 
the  following  considerations:  (1)  Previous  workers  in  the  Little  Belt 
Mountains  place  the  date  of  the  last  uplift  in  this  general  region  at 
the  close  of  the  Miocene.  After  this  period  the  region  was  base-leveled. 
Whether  the  oldest  terrace  was  formed  as  a result  of  this  base-leveling 
or  at  some  later  period  is  not  known,  but  it  is  certain  that  it  was  not 
earlier  than  the  close  of  Miocene  time.  (2)  Terrace  gravel  believed  to 
be  contemporaneous  with  the  oldest  deposits  here  described  occurs 
northwest  of  Great  Falls,  on  the  high  divide  between  Sun  and  Teton 
rivers,  a few  miles  beyond  the  area  to  which  this  report  relates. 
(3)  In  the  bottom  of  Sun  River  valley  near  Augusta,  at  least  300  feet 
below  the  highest  gravel  terrace  to  the  north,  terminal  moraines  of 
mountain  glaciers  are  found.  According  to  Calhoun,®  in  the  region 

a Calhoun,  F.  H.  H.,  The  Montana  lobe  of  the  Keewatin  ice  sheet : Prof.  Paper  U.  S.  Geol.  Survey  No. 
50,  1900,  p.  46. 


STRATIGRAPHY. 


41 


to  the  north  material  derived  from  local  glaciers  is  overlain  by  de- 
posits of  the  continental  ice  sheet,  and  from  this  and  other  observa- 
tions made  throughout  the  general  region  to  the  north  he  regards  the 
local  glaciers  of  the  Lewis  Range  as  but  slightly  older  than  those  of 
the  Keewatin  ice  sheet,  which  occupied  this  area  during  Wisconsin 
time.  Prior  to  both  the  local  and  continental  glaciation  of  this  re- 
gion, therefore,  a period  must  have  elapsed  sufficient  for  the  erosion 
of  Sun  River  valley  nearly  to  its  present  stage  after  the  gravel  cap- 
ping the  high  divide  between  Sun  and  Teton  rivers  was  laid  down. 
The  erosion  of  this  valley  required  considerable  time,  so  that  it  seems 
probable  that  the  high  terrace  gravels  north  of  Sun  River,  which  are 
believed  to  be  contemporaneous  with  the  older  terrace  gravels  in  the 
area  described,  should  be  regarded  as  of  early  Quaternary  or  possibly 
late  Tertiary  age. 

GLACIAL  DEPOSITS. 

General  statement. — Glacial  deposits  of  Wisconsin  age  occupy  a 
considerable  area  throughout  the  Great  Falls  region.  The  terminal 
moraine  of  the  Montana  lobe  of  the  Keewatin  ice  sheet  enters  the  dis- 
trict at  a point  about  10  miles  due  northeast  of  Great  Falls,  extending 
southward  across  Missouri  River  to  Sand  Coulee  near  Gerber  station. 
At  this  point  it  makes  a sharp  bend  to  the  east  and  continues  thus 
past  the  head  of  Red  Coulee,  thence  northeastward  to  Belt  Creek, 
where  it  crosses  the  northeastern  margin  of  the  district.  Its  location 
and  extent,  as  first  worked  out  by  Calhoun®  and  later  examined  more 
in  detail  by  the  writer,  are  shown  on  the  geologic  map  (PI.  I).  In 
addition  to  the  morainal  deposits,  extensive  lake  sediments  were  laid 
down  in  front  of  the  terminal  moraine  during  the  occupation  of  this 
general  region  by  the  ice.  Much  of  this  material  has  been  removed 
by  postglacial  erosion,  especially  on  the  higher  lands,  but  all  the  larger 
valleys  in  front  of  the  moraine  are  filled  with  it.  Lake  deposits  of  two 
different  periods,  an  earlier  and  a later,  have  been  recognized  by  gla- 
ciologists in  this  region.  The  limits  of  the  earlier  lake  can  be  ascer- 
tained only  by  bowlders  lodged  on  the  summits  of  the  plateaus,  but  a 
considerable  part  of  the  deposits  of  the  more  recent  lake  still  remains 
as  a filling  in  the  larger  valleys. 

Drift. — The  drift  consists  of  crystalline  erratics,  small  pebbles, 
sedimentary  rocks,  and  a matrix  of  sand  and  clay.  The  greater  part  of 
the  material,  however,  is  a sandy  clay  of  dull-green  color,  generally 
unstratified,  %vhich  stands  in  vertical  faces  where  trenched  by  streams. 
The  character  of  the  rocks  composing  the  drift  has  been  studied  in 
detail  by  Calhoun,6  who  describes  them  as  follows: 

The  crystalline  erratics  are  of  such  variety  as  to  furnish  specimens  of  the  whole  rock 
series.  In  a small  area,  not  over  5 square  yards  in  extent,  the  following  rocks  were 
found:  Limestone,  sandstone,  shale,  coal,  granites  (both  fine  and  coarse  grained  and 


a Op.  cit.,  PI.  V. 


&Op.  cit.,  p.  27. 


42 


GEOLOGY  OF  GREAT  FALLS  COAL  FTELD,  MONTANA. 


with  different  percentages  of  quartz  and  feldspar),  syenites,  diorites,  basalts,  and 
hornblende,  mica,  and  garnetiferous  schist,  and  all  gradations  between  these  and 
gneissic  rocks.  The  granite  and  the  syenite  rocks  predominate.  Basalt  and  rocks 
containing  a large  proportion  of  the  ferromagnesian  minerals  are  not  so  common. 

In  his  general  study  of  the  Montana  lobe  of  the  Keewatin  ice  sheet 
Calhoun  observes  little  variation  in  the  nature  of  the  bowlders 
throughout  the  length  of  the  moraine.  Limestone  bowlders  are  more 
common  in  the  northern  part  and  sandstone  bowlders  in  the  southern 
part,  but  the  character  of  the  crystalline  bowlders  remains  the  same. 
The  small  pebbles  which  make  up  a varying  proportion  of  the  bowl- 
ders of  the  drift  are  believed  by  Calhoun  to  be  of  mountain  origin, 
having  been  derived  from  a quartzite  gravel  formation  to  the  north- 
east. Crystalline  bowlders  are  generally  common  on  the  surface  of  the 
drift,  but  in  the  body  of  the  material  not  many  are  found.  Here  even 
smaller  pebbles  sparingly  occur.  An  explanation  of  the  position  of 
these  bowlders  in  the  drift  is  given  by  It.  D.  Salisbury.®  The  thick- 
ness of  the  drift  within  the  area  treated  is  variable,  the  maximum 
observed  being  between  150  and  200  feet. 

Lake  sediments. — The  lake  deposits  are  mainly  of  two  kinds — large 
bowlders  deposited  on  the  high  land  by  floating  ice  in  waters  of  the 


Fig.  1.— Ideal  cross  section  showing  relations  between  the  two  lake  deposits  in  Missouri  River  val- 
ley west  of  Great  Falls,  c,  Level  of  the  more  extended  lake;  d,  level  of  the  smaller  lake.  After 
Calhoun. 

older  and  more  extensive  lake  and  finely  laminated  sandy  clay  laid 
down  by  the  smaller  lake  in  the  larger  valleys  of  the  Great  Falls 
region  (figs.  1 and  2).  A detailed  examination  of  the  composition  of 
these  lake  sediments  was  not  made  by  the  writer,  but  they  were  care- 
fully studied  by  Calhoun,  whose  description  is  here  given.6 

The  deposits  of  the  more  restricted  lake  consist  of  a finely  laminated  clay  which 
when  dry  is  hard  and  cleaves  like  shale.  When  wet  it  becomes  soft  and  pliable,  and 
would  make  an  excellent  molding  clay.  Interstratified  with  the  clay  are  small  crystal- 
line pebbles  one-fourth  to  one-half  inch  in  thickness.  They  usually  consist  of  quartz 
or  feldspar  crystals,  or  of  small  fragments  containing  several  minerals,  showing  that  the 
rock  from  which  they  were  derived  was  granite,  syenite,  or  basalt.  Very  seldom  a 
large  crystalline  bowlder  is  found  embedded  in  the  clay. 

The  maximum  thickness  of  this  clay  within  the  area  treated  was  not 
ascertained,  but  along  the  Missouri  near  Ulm  Calhoun  observed c a 
thickness  of  40  feet,  the  material  containing  the  small  crystalline  peb- 
bles characteristic  of  the  formation  farther  north.  Its  distribution  is 
not  shown  separately  on  the  geologic  map,  as  it  is  included  with  the 
alluvium.  The  accompanying  ideal  sections  (figs.  1 and  2)  by  the 

U Jour.  Geology,  vol.  8,  1900,  pp.  426-432.  f>Op.  cit.,  pp.  30-31.  ‘ Op.  cit.,  p.  31. 


STRATIGRAPHY. 


48 


above-named  author®  illustrate  the  relation  of  the  two  lake  deposits  to 
the  drift  and  ice  dam. 


ALLUVIUM. 

General  statement. — The  alluvial  deposits  of  the  Great  Falls  region 
present  rather  unusual  features.  They  occur  intimately  associated 
with  glacial-lake  sediments  of  the  Keewatin  ice  sheet,  and  on  the 
geologic  map  are  not  differentiated  from  those  sediments.  As  pre- 
viously stated,  during  the  occupation  of  the  region  by  the  continental 
glaciers  the  waters  of  the  Missouri  and  its  larger  tributaries  were 
dammed  and  an  extensive  lake  existed  first  in  front  of  the  ice  and 
later  in  front  of  the  terminal  moraine.  Sediments  of  this  lake  in  its 
various  stages  filled  all  the  larger  valleys  in  the  vicinity  of  Great  Falls. 
Although  much  of  the  material  constituting  these  sediments  was 
brought  down  by  streams  from  adjoining  mountainous  region,  and  to 
this  extent  they  correspond  to  normal  alluvial  deposits  along  any 
large  stream,  a certain  amount  was  contributed  by  the  melting  ice 
from  the  glacier.  The  alluvium,  therefore,  of  the  Missouri  and  its 
larger  tributaries  in  this  immediate  district  has  been  derived  from 


Fig.  2. — Ideal  longitudinal  section  showing  the  relation  of  the  two  lake  deposits  shown  in  fig.  1 to 
the  drift  dam  and  the  ice  dam.  a,  Ice  edge;  b,  moraine;  c,  level  of  the  more  extended  lake;  d,  level 
of  the  smaller  lake.  After  Calhoun. 

two  distinct  sources.  That  brought  in  by  the  river  may  be  regarded  as 
local  and  that  by  the  glacier  as  foreign. 

Character  and  extent. — The  alluvium  of  the  Missouri,  together  with 
that  of  Sun  and  Smith  rivers,  its  principal  tributaries,  ranges  from 
half  a mile  to  3 miles  in  width.  It  consists  mainly  of  fine  silt  and  sand, 
with  local  beds  of  clay  and  gravel.  Light  colors  prevail  throughout 
the  material.  F rom  the  base  of  the  Big  Belt  Mountains  northeastward 
to  Great  Falls  the  Missouri  meanders  through  a wide  flood  plain  of 
an  old  valley,  but  east  of  Great  Falls  it  flows  through  a narrow  valley 
which  is  much  younger  and  in  which  only  small  detached  areas  of 
alluvium  are  found.  Alluvial  deposits  of  small  extent  occur  along 
Belt  Creek  and  all  the  minor  streams,  but  these  are  not  shown  on  the 
geologic  map. 

DUNE  SAND. 

Character  and  extent. — Deposits  of  dune  sand  occupy  a number  of 
small  areas  in  the  vicinity  of  Great  Falls.  They  are  confined  mainly  to 
the  Missouri  River  valley,  but  some  are  found  on  the  lower  plateaus 
bordering  the  streams.  These  areas,  though  small,  present  the 
characteristic  dune-sand  topography  of  hillocks  and  basins  with  no 


4 «Op.  cit.,  p.  30. 


44  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

developed  drainage.'  The' dunes  range  from  10  to  20  feet  in  width. 
They  are  of  recent  origin  and  in  many  places  travel  before  the  wind. 
Perhaps  the  largest  accumulation  of  these  deposits  occurs  about  1 
mile  southeast  of  Great  Falls,  on  a plateau  of  the  Kootenai  rocks 
which  lies  approximately  100  feet  above  the  town.  Here  a belt  of  low 
sand  hills  nearly  one-half  mile  in  width  extends  for  1 1 miles  in  a north- 
easterly direction.  Another  noteworthy  dune  area  is  on  the  west  side 
of  the  Missouri  River  valley  about  4 miles  above  the  mouth  of  Sand 
Coulee.  Smaller  areas  are  to  be  found  in  the  larger  bends  of  Missouri 
River  between  Great  Falls  and  Cascade.  In  the  valley  on  the  west 
side  of  Smith  River,  near  the  confluence  of  that  stream  with  the 
Missouri,  there  are  deposits  of  sand  which  have  been  blown  about  by 
the  wind  but  have  not  been  formed  into  distinct  dunes.  At  many 
places  throughout  the  flood  plain  of  the  Missouri  sagebrush  and  other 
small  shrubs  hold  the  sandy  soil  about  their  roots  and  collect^&d- 
ditional  material  blown  about  by  small  wind  currents  to  suoter  an 
extent  that  mounds  1 to  2 feet  high  are  built  up  about  each  bush, 
giving  the  appearance  of  miniature  dune-sand  topography.  The  dis- 
tribution of  the  eolian  deposits  is  not  shown  on  the  map. 

Source. — The  dune  sand  of  the  Great  Falls  region  is  derived  prin- 
cipally from  alluvial  deposits  of  the  Missouri  Valley.  It  consists 
mainly  of  loose,  fine-grained  sand  which  in  many  places  is  not  covered 
by  vegetation,  so  that  it  is  readily  caught  up  by  the  wind  and  carried 
about.  The  sand  thus  transported  is  generally  redeposited  in  the 
form  of  dunes  in  the  valley  or  on  the  slopes  of  the  adjoining  highlands, 
but  sometimes  it  is  blown  out  of  the  valley  and  lodged  on  the  bluffs 
above.  It  is  believed  that  the  deposits  south  of  Great  Falls  originated 
in  this  way. 

IGNEOUS  ROCKS. 

Igneous  rocks  occur  in  the  Great  Falls  region  mainly  in  the  form  of 
dikes  and  sheets,  although  stocks  and  unexposed  laccoliths  are  also 
to  be  found.  The  dike  rock  of  most  common  occurrence  is  a basalt, 
of  which  there  are  a number  of  varieties.  It  is  usually  very  dark 
colored  and  dense,  presenting  on  the  surface  a spotted  appearance, 
due  to  the  presence  of  large  crystals  of  basaltic  augite.  Much  of  the 
intruded  material  is  sufficiently  hard  to  resist  weathering  better 
than  the  soft  sedimentary  rocks  and  stands  out  as  an  irregular  wall  or 
ridge.  Less  commonly  the  intrusive  material  is  soft  and  crumbles 
easily,  so  that  it  can  be  traced  only  by  lines  of  green  vegetation 
growing  on  the  surface  of  the  decomposed  rock.  Rocky  Ridge  is 
formed  by  one  of  the  harder  basaltic  dikes  extending  from  a point 
near  the  base  of  Highwood  Mountains  southwest  to  V illiams  Creek. 
The  intrusive  rocks  in  this  region  do  not,  so  far  as  known,  cut  or 
disturb  to  any  considerable  extent  the  areas  underlain  by  workable 


STRATIGRAPHY. 


45 


coal,  and  consequently  they  are  not  of  very  great  importance  in  the 
present  discussion.  In  several  places,  however,  intrusives  appear 
at  the  surface  on  the  margin  of  areas  believed  to  be  underlain  by 
workable  coal,  notably  on  the  northern  border  of  the  Otter  Creek 
coal  area,  near  the  mouth  of  Williams  Creek,  on  the  upper  part  of 
Hazlett  Creek,  on  the  west  side  of  the  Sage  Creek  coal  area,  and  on 
the  northeast  side  of  Belt  Butte  along  the  east  side  of  the  Sand 
Coulee  coal  area.  In  none  of  these  localities  can  the  intrusive  rocks 
be  traced  by  surface  outcrops  into  the  area  underlain  by  workable  coal; 
but  they  may  possibly  continue,  although  unexposed,  sufficiently 
far  to  cut  and  disturb  valuable  coal  beds.  Xo  special  examination 
was  jnade  of  the  petrographic  character  of  the  intrusive  rock  in  the 
eastern  part  of  the  Great  Falls  field,  for  it  forms  a portion  of  a large 
petr^raphie  province  of  central  Montana  which  has  been  studied  in  a 
detailed  and  comprehensive  way  by  Weed  and  Pirsson.  For  a more 
extensive  account  of  these  rocks  and  of  the  larger  petrographic  prov- 
inc%*if  which  they  form  a part,  the  reader  is  referred  to  the  following 
publications: 

Weed,  W.  H.  Two  Montana  coal  fields:  Bull.  Geol.  Soc.  America,  vol.  3,  1892, 
pp.  301-330. 

Little  Belt  Mountains  folio  (Xo.  56),  Geologic  Atlas  U.  S.,  U.  S.  Geol.  Survey, 

1899. 

Geology  of  the  Little  Belt  Mountains,  Montana:  Twentieth  Ann.  Rept.  U.  S. 

Geol.  Survey,  pt.  3,  1900,  pp.  271-461. 

Weed,  W.  H.,  and  Pirsson,  L.  Y.  Igneous  rocks  of  Yogo  Peak,  Montana:  Am. 

Jour.  Sci.,  3d  ser.,  vol.  50,  1895,  pp.  467^79. 

Highwood  Mountains  of  Montana:  Bull.  Geol.  Soc.  America,  vol.  6, 

1895,  pp.  389-422. 

Geology  of  the  Castle  Mountain  mining  district,  Montana:  Bull.  U.  S. 

Geol.  Survey,  No.  139,  1896. 

The  Bearpaw  Mountains,  Montana:  Am.  Jour.  Sci.,  4th  ser.,  vol..  1 

1896,  pp.  283-301,  351-362;  vol.  2,  1896,  pp.  136-148,  188-199. 

Missourite,  a new  leucite  rock  from  the  Highwood  Mountains  of 

Montana:  Am.  Jour.  Sci.,  4th  ser.,  vol.  2,  1896,  pp.  315-323. 

Geology  of  the  Little  Rocky  Mountains:  Jour.  Geolog}’,  vol.  4,  1896, 

pp.  399-428. 

Geology  and  mineral  resources  of  the  Judith  Mountains  of  Montana: 

Eighteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3,  1898,  pp.  446-616. 

Pirsson,  L.  V.  Petrography  of  the  igneous  rocks  of  the  Little  Belt  Mountains,  Mon- 
tana: Twentieth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3,  1900,  pp.  463-581. 

Petrography  and  geology  of  the  igneous  rocks  of  the  Highwood  Mountains, 

Montana:  Bull.  U.  S.  Geol.  Survey  No.  237,  1905. 

In  the  vicinity  of  Cascade,  Mont.,  on  the  eastern  side  of  Missouri 
River,  in  sec.  20,  T.  17  N.,  R.  1 E.,  a large  dike  extends  into  the  area 
from  the  main  bed  of  intrusive  rock  constituting  the  north  end  of 
the  Big  Belt  Mountains.  As  this  dike  radiates  from  an  igneous 
mass  at  a considerable  distance  from  those  above  described,  samples 
from  it  were  collected  for  the  purpose  of  having  thin  sections  prepared 


46 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


and  studied.  These  sections  have  been  examined  by  Albert  Johann- 
sen,  of  the  Geological  Survey,  whose  preliminary  report  is  as  follows: 

Tentative  name:  Andesite  porphyry  with  latite  affinities. 

Megascopic:  A dark-gray  porphyritic  rock,  weathering  a dirty  yellow.  The  black 
phenocrysts,  up  to  one-eighth  inch  in  diameter,  become  very  pronounced  on  the 
weathered  surface. 

Microscopic:  Porphyritic;  about  one-fifth  phenocrysts.  The  groundmass  has  an 
intersertal  texture  in  which  the  irregular  areas  are  of  a dirty-brown  serpentine.  The 
phenocrysts,  which  are  chiefly  augite,  are  generally  in  broad,  lath-shaped  sections.  A 
few  of  the  feldspar  crystals  of  the  groundmass  are  larger  than  the  remainder  and  may 
be  classed  with  the  phenocrysts.  The  groundmass  consists  of  dirty  yellowish-brown 
serpentine,  less  augite,  about  the  same  amount  of  magnetite,  much  less  orthoclase, 
and  some  pseudomorphs,  now  serpentine,  which  have  the  form  of  olivine.  The  feld- 
spar consists  of  plagioclase  and  orthoclase;  the  plagioclase  varies  in  composition  from 
andesine  to  andesine  labradorite.  Apparently  none  is  more  basic  than  Ab50,  An50. 
The  index  of  refraction  is  ±551. 

MET  AMORPHIC  ROCKS. 

Very  few  metamorphic  rocks  are  found  in  the  plains  portion  of  the 
Great  Falls  region,  although  in  the  mountainous  districts  surrounding 
the  field  the  sedimentary  rocks  have  been  highly  metamorphosed  by 
intrusive  dikes,  sheets,  and  laccoliths.  The  Highwood  Mountains 
bordering  this  field  on  the  north  have  been  caused  by  igneous  intru- 
sion in  Cretaceous  rocks,  which  were  metamorphosed  to  such  an 
extent  that  they  have  resisted  subsequent  erosion  and  now  stand  out 
from  the  surrounding  plains  as  a cluster  of  high  peaks.  Intrusions 
in  the  form  of  stocks  and  laccoliths  are  more  or  less  common  along 
the  base  of  the  adjoining  mountain  ranges.  From  some  of  these 
intruded  rock  masses  the  overlying  sediments  have  been  removed, 
exposing  a central  core  of  igneous  rock,  around  which  contact-meta- 
morphic  phenomena  are  well  exhibited.  A good  illustration  of  these 
conditions  is  found  on  the  east  side  of  Little  Otter  Creek,  about  3 
miles  south  of  Mann,  outside  of  the  area  here  discussed. 

As  previously  stated,  intrusive  rock  in  this  district  is  most  com- 
monly found  in  the  form  of  dikes.  In  most  localities  these  have 
metamorphosed  the  sediments  into  which  they  were  intruded  for 
some  distance  back  from  the  contact,  converting  sandstone  into 
quartzite  and  shale  into  slate.  Phenomena  of  this  character  were 
observed  at  several  places,  notably  on  the  north  side  of  the  Big  Belt 
Mountains,  about  7 miles  southwest  of  Orr,  in  the  vicinity  of  Rocky 
Ridge,  and  throughout  that  portion  of  the  field  which  lies  east  of 
Stanford.  No  places  were  observed  where  the  intrusives  had  cut 
the  workable  coals  and  thereby  altered  them  by  metamorphism  along 
the  contact.  For  this  reason  no  special  study  was  made  of  the 
character  of  the  contact-metamorphic  rocks  of  the  field.  It  is  highly 
probable  that  the  intrusives  which  cut  the  sediments  on  the  northeast 
side  of  Belt  Butte  have  had  some  effect  on  the  Kootenai  coals  of  that 


STRUCTURE. 


47 


district,  providing  they  extend  so  far  east,  but  as  there  are  no  expo- 
sures of  the  coal  beds  the  phenomena  could  not  be  observed.  There 
are  also,  on  the  upper  part  of  Hazlett  Creek,  dikes  which  in  their 
northeast  extension  may  cut  and  alter  by  metamorphism  workable 
coals,  but  these  dikes  could  not  be  traced  on  the  surface  into  the  coal 
area.  The  same  is  true  of  the  dike  forming  Rocky  Ridge,  which 
extends  southward  from  Highwood  Mountains,  but  disappears  at  the 
northern  edge  of  the  Otter  Creek  coal  area. 

STRUCTURE. 

PLAINS  PROVINCE. 

GENERAL  CONDITIONS. 

Throughout  the  plains  portion  of  the  region  described  the  structure 
is  relatively  simple.  The  rocks  as  a rule  lie  nearly  horizontal,  dipping 
with  a small  angle  to  the  north  and  east,  away  from  the  mountains, 
but  in  the  mountainous  portion  the  structure  is  more  complex.  Al- 
though low  dips  of  3°  to  5°  prevail  throughout  the  plains  province,  and 
the  district  is  one  of  little  disturbance,  the  rocks  on  closer  examination 
are  found  to  be  gently  folded  into  a series  of  shallow  synclines  and  low 
anticlines.  This  structural  feature  is  scarcely  perceptible  to  the  cas- 
ual observer,  being  revealed  only  by  a careful  examination  of  the  beds 
exposed  along  the  sides  of  the  larger  streams,  such  as  Otter  and  Belt 
creeks  and  Smith  River  and  its  principal  tributaries.  The  major  axes 
of  these  folds  appear  to  be  roughly  parallel  to  the  Little  Belt  Moun- 
tains uplift,  but  the  folds  are  only  of  slight  magnitude  and  the  indi- 
vidual warps  are  broad.  The  largest  and  most  perceptible  of  the 
synclinal  depressions  crosses  Otter  Creek  between  the  mouth  of  Wil- 
liams Creek  and  the  Nollar  mine.  Its  effect  is  to  carry  the  coal-bear- 
ing rocks  of  the  Otter  Creek  area  about  100  feet  below  Otter  Creek 
valley  for  a distance  of  3 or  4 miles. 

The  slight  deformation  of  the  coal-bearing  rocks  has  had  an  impor- 
tant bearing  on  the  development  of  the  coal  beds  of  this  field.  Wher- 
ever stream  valleys  cross  the  coal-bearing  areas  and  cut  sufficiently 
deep  to  expose  the  coal,  they  produce  favorable  conditions  for  mining. 
Owing  to  the  horizontal  position  of  the  beds,  entries  can  be  driven  for 
long  distances  nearly  at  right  angles  to  the  direction  of  the  dip,  which 
is  in  general  to  the  north,  without  producing  an  appreciable  lift  in  the 
haulage  of  the  coal.  The  gentle  northward  dip  of  the  coal-bearing 
rocks  can  be  turned  to  advantage  in  mining  by  driving  the  main  entry 
at  an  angle  greater  than  90°  with  the  direction  of  the  dip,  thus  causing 
the  entry  to  extend  up  the  dip  sufficiently  to  produce  natural  drain- 
age of  the  workings.  Though  in  general  the  rocks  lie  nearly  hori- 
zontal throughout  the  Great  Falls  field,  there  are  minor  undulations  in 
the  strata  which  are  too  local  to  be  observed  on  the  surface,  but  which 


48 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


are  shown  in  the  maps  of  the  mine  workings.  Some  of  these  cause 
more  or  less  difficulty  in  mine  haulage,  making  it  necessary  to  use 
special  appliances  to  fit  the  topographic  conditions  in  the  mine. 

DOMES. 

Local  doming  of  the  strata,  due  to  laccolithic  intrusion  of  igneous 
rock,  is  more  or  less  common  along  the  north  side  of  the  Little  Belt 
Mountains  and  in  the  vicinity  of  the  Judith  Mountains,  farther  east. 
Skull  Butte,  in  the  plains  province  at  the  east  end  of  the  district,  is  with- 
out doubt  a domal  uplift  of  this  character.  It  is  nearly  circular  in  out- 
line, its  greatest  diameter  being  about  1J  miles,  and  its  quaquaversal 
dips  ranging  from  20°  to  30°.  Erosion  of  its  center  has  not  advanced 
sufficiently  to  uncover  igneous  rocks.  This  uplift  exposes  the  coal  in 
the  steeply  dipping  beds  about  its  base. 

In  the  vicinity  of  Stockett  local  uplift  and  erosion  occurred  prior  to 
the  deposition  of  Jurassic  sediments,  as  is  shown  by  the  unconformable 
relations  of  Jurassic  sandstone  and  Madison  limestone.  Exposures  of 
the  limestone  occur  in  which  the  strata  are  tilted  and  eroded,  with 
Jurassic  sandstone  deposited  across  the  upturned  ends.  The  strongest 
dip  of  the  limestone  beds  seen  was  about  10°.  The  various  forma- 
tions in  this  vicinity  are  perceptibly  thinner  than  elsewhere,  a strati- 
graphic feature  probably  due  to  the  presence  of  the  dome  during  the 
deposition  of  these  sediments.  The  unconformable  relations  of  the 
Carboniferous  and  Jurassic  formations,  and  the  moderately  steep  dips 
of  the  latter  as  exhibited  in  Sand  Coulee,  about  2 miles  east  of  Stock- 
ett, are  shown  in  PI.  YI.  This  doming  of  the  Carboniferous  rocks  in 
the  Stockett  region  is  probably  not  of  wide  extent,  but  its  exact  limits 
can  not  be  ascertained  owing  to  the  lack  of  exposures.  Its  north- 
south  dimension,  as  shown  by  outcrops  along  Sand  Coulee,  is  about  4^ 
miles,  but  its  east  and  west  boundaries  are  not  known.  At  Stockett 
and  along  Sand  Coulee  valley,  owing  to  the  thinning  of  the  Jurassic 
and  Lower  Cretaceous  formations,  also  to  the  absence  of  the  Quadrant 
in  the  vicinity  of  the  dome,  the  coal  horizon  occurs  only  about  150  feet 
above  the  Madison  limestone,  which  is  exposed  in  the  bottom  of  the 
valley.  This  feature  might  be  misleading  to  prospectors  who  are  not 
familiar  with  the  local  conditions  about  Stockett,  for  in  other  parts  of 
the  Great  Falls  coal  field,  especially  along  Belt  Creek  and  in  the  Otter 
and  Sage  Creek  areas,  the  coal  bed  is  separated  from  the  Madison 
limestone  by  about  650  feet  of  rock. 

At  the  head  of  Ming  Coulee,  where  coal  of  workable  thickness  is 
exposed,  the  beds  dip  steeply  to  the  northwest.  These  local  dips  are 
due  to  a large  dome  farther  south,  outside  of  the  area  treated  in  this 
report.  The  Quadrant  formation  is  also  absent,  causing  the  coal  bed 
to  occur  about  250  feet  above  the  top  of  the  Madison. 


STRUCTURE. 


49 


On  Boston  Coulee,  about  2|  miles  west  of  Eden,  a local  dome  of  the 
strata  exposes  the  coal-bearing  bed  along  Boston  Coulee  for  about  1J 
miles,  and  also  to  the  southward  up  a small  tributary  of  that  coulee  for 
an  equal  distance.  This  small  uplift,  which  causes  the  coal  outcrop  to 
take  a T-shaped  form,  is  shown  on  the  coal  map  (PI.  II). 

FAULTS. 

No  large  faults  occur  within  the  area  here  discussed,  but  minor 
faults  are  not  uncommon,  especially  in  the  vicinity  of  Belt  and  Stock- 
ett.  The  throw  of  these  faults  ranges  from  5 to  20  feet,  and  their 
presence  is  usually  difficult  to  detect  on  the  surface.  They  are  gen- 
erally first  encountered  by  miners  who  are  working  the  coal  bed,  and 
in  some  places  their  presence  has  caused  considerable  difficulty  in  min- 
ing operations.  At  Belt,  on  the  west  side  of  Belt  Creek,  such  a fault 
extends  nearly  west  for  about  1J  miles,  displacing  the  coal  bed  a few 
feet  and  causing  difficulty  in  operations  along  the  north  side  of  the 
underground  workings  of  the  Anaconda  Copper  Mining  Company’s 
mine.  In  Armington  Coulee,  about  half  a mile  above  the  mouth,  a 
sharp  fold  in  the  beds  trends  northward  toward  Belt  Butte.  The  beds 
may  possibly  be  more  or  less  fractured  along  its  axis,  but  exposures  at 
this  place  were  inadequate  for  positive  determination  of  this  point. 
Other  small  displacements  have  been  reported  from  some  of  the 
smaller  mines  along  the’ east  side  of  Belt  Creek  in  the  vicinity  of  Arm- 
ington and  Belt,  notably  in  the  Richardson  mine  and  to  a less  degree 
in  the  Smauch  and  Millard  mines,  but  these  faults  appear  not  to  cause 
any  appreciable  displacement  of  the  sediments  at  the  surface.  On  the 
north  side  of  Stockett  a small  fault  in  the  Madison  limestone  has  a 
throw  of  about  15  feet,  extending  east  and  west.  The  Cottonwood 
Coal  Company  reports  that  a small  north-south  fault  in  the  coal-bear- 
ing rocks  was  encountered  in  mining  about  three-fourths  of  a mile  east 
of  the  town;  but  no  evidence  of  this  fault  was  observed  on  the  surface. 
The  minor  faults  throughout  the  Great  Falls  coal  field  are  not  shown 
on  the  geologic  map.  It  is  possible  that  many  such  small  faults  are 
scattered  over  the  field  and  will  be  discovered  on  more  extensive 
development  of  the  coal  deposits,  but  it  is  difficult  if  not  impossible  to 
locate  them,  owing  to  the  fact  that  their  throw  is  generally  insufficient 
to  be  perceptible  on  the  surface. 

LITTLE  BELT  MOUNTAINS. 

The  general  structure  of  the  Little  Belt  Mountains,  which  border 
this  area  on  the  south,  is  that  of  an  anticlinal  uplift  with  sharply  dip- 
ping sides  and  a flat  summit.  In  the  central  portion  of  the  range  the 
stratified  rocks  lie  nearly  horizontal,  but  along  the  northern  flank  of 
54937— Bull.  356—09 4 


50  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

the  uplift,  as  found  on  the  head  of  Geyser  Creek,  the  limestone  dips  at 
an  angle  of  15°  to  20°  toward  the  lower  plains  country.  As  previously 
stated,  the  simple  structure  of  the  northern  part  of  the  uplift  has  been 
considerably  modified  by  the  intrusion  of  igneous  rocks  in  the  form  of 
laccoliths,  which  have  caused  local  doming  of  the  strata  in  many 
places.  Only  one  of  these  laccolithie  domes  lies  within  the  area  de- 
scribed, but  there  are  others,  such  as  those  east  of  Kibby  and  in  the 
head  of  Dry  Wolf  Creek,  whose  marginal  structure  extends  into  the 
district.  In  the  vicinity  of  the  larger  intruded  masses  of  igneous  rock 
the  dips  are  in  many  places  steep  and  variable,  but  in  that  portion  of 
the  mountain  front  where  local  intrusions  have  not  disturbed  the 
strata,  they  dip  away  normally  from  the  uplift  at  angles  of  6°  to  12°, 
lessening  gradually  toward  the  lower  plains  country. 

HIGHWOOD  MOUNTAINS. 

The  Highwood  Mountains,  which  border  on  the  north  the  east  end  of 
the  area  described  in  this  report,  are  structurally  of  a different  type 
from  the  Little  Belt  Range.  They  consist  of  a group  of  isolated  peaks, 
which  were  formed  by  igneous  intrusions  in  Cretaceous  rocks  that  were 
horizontally  bedded  or  slightly  inclined  toward  the  east.  Subsequent 
to  this  intrusion  stream  erosion  carved  out  this  cluster  of  peaks  from 
the  surrounding  plains. 

ECONOMIC  GEOLOGY. 

GENERAL  STATEMENT. 

The  mineral  resources  of  the  area  treated  in  this  report  are  some- 
what varied,  but  the  principal  one  at  present  is  coal.  Fire  clay  of  a 
superior  quality  is  found  in  beds  of  workable  thickness  along  Belt 
Creek  and  its  tributaries,  and  at  many  places  throughout  the  district 
raw  materials  suitable  for  the  manufacture  of  Portland  cement  can 
be  obtained.  Gypsum  deposits  occur  at  different  horizons  in  the 
Quadrant  formation  near  Riceville,  and  at  Goodman  this  mineral 
has  been  mined  in  a small  way  for  a number  of  years.  Building 
stones  of  different  varieties,  also  limestone,  are  common  in  many 
parts  of  the  field.  Sand  and  gravel  can  usually  be  obtained  locally. 
Iron  pyrite  is  mined  as  a by-product  with  the  coal  and  shipped  to 
Great  Falls,  where  it  is  used  in  the  process  of  pyritic  smelting. 

COAL. 

GEOLOGIC  OCCURRENCE. 

Throughout  the  Great  Falls  coal  field  the  coal  occurs  in  the  lower 
part  of  the  Kootenai,  or  Lower  Cretaceous  rocks,  mainly  at  a horizon 
about  60  feet  above  the  base  of  the  formation.  Coal  of  workable 
thickness  is  not  continuous,  however,  at  this  horizon,  but  varies 
locally. 


COAL. 


51 


This  irregularity  of  occurrence  is  a characteristic  feature  of  the 
beds  of  this  field  which  was  early  observed  in  the  investigation,  and 
an  effort  was  made  to  ascertain  as  far  as  possible,  from  a study  of  the 
outcrop,  the  limits  of  the  areas  underlain  by  workable  coal.  These 
coal  areas,  or  basins,  as  they  have  previously  been  designated  by 
Weed,®  are  three  in  number  and  include  a total  area  of  approximately 
334  square  miles.  The  largest,  comprising  about  231  square  miles, 
lies  south  of  Great  Falls,  extending  from  a point  a short  distance  east 
of  Belt  Creek  beyond  Smith  River.  (See  PI.  II.)  It  is  possible  that 
the  coals  of  this  basin  continue  to  the  south  throughout  the  territory 
lying  between  the  Little  and  Big  Belt  mountains,  but  no  examination 
was  made  of  this  region.  The  district  examined  is  drained  by  Sand 
Coulee  and  its  tributaries,  and  is  known  as  the  Sand  Coulee  area. 
To  the  east  the  next  district  underlain  by  coal  of  commercial  impor- 
tance lies  between  Little  Otter  and  Geyser  creeks,  and  is  designated 
the  Otter  Creek  area;  it  is  the  smallest  coal  area  in  the  field,  includ- 
ing only  about  37  square  miles.  Still  farther  east,  in  the  vicinity  of 
Skull  Butte,  there  is  a third  coal  area,  which,  owing  to  its  nearness 
to  Sage  Creek,  the  main  drainage  channel  of  the  district,  is  called  the 
Sage  Creek  area.  It  includes  about  66  square  miles. 

SAND  COULEE  AREA. 

LOCATION  AND  EXTENT. 

The  Sand  Coulee  coal  area,  which  lies  south  of  Great  Falls,  is  6 
miles  wide  and  from  30  to  40  miles  long.  The  exact  limits  of  the 
area  underlain  by  workable  coal  are  difficult  to  determine,  for  it  is 
only  along  the  valleys  of  streams  that  cross  the  area,  such  as  Belt 
Creek,  Sand  Coulee,  and  Smith  River  and  their  tributaries,  that  the 
coal  bed  can  be  studied  with  respect  to  its  disposition  to  thicken  or 
thin  in  any  given  direction.  In  the  plateau  district  between  these 
valleys  the  coal  is  concealed  by  200  to  300  feet  of  overlying  Kootenai 
rocks,  wffiich  the  smaller  streams  traversing  the  plateaus  have  not 
cut  down  sufficiently  to  expose  the  coals.  As  the  rocks  dip  gently 
away  from  the  mountains,  the  outcrop  of  the  coal  bed  extending 
across  the  plateau  from  one  stream  valley  to  another  occurs  far  up 
the  slope  in  the  foothill  zone,  where  the  coal  is  usually  represented 
by  a thin  bed  of  carbonaceous  shale.  Under  these  conditions  it  is 
apparent  that  the  width  of  the  coal  basin  can  only  be  inferred  from 
the  thickness  of  the  beds  along  the  stream  valleys.  As  these  valleys 
are  more  or  less  widely  separated,  the  lateral  extent  of  the  coal  area 
in  the  plateau  region  is  largely  conjectural. 

Along  Belt  Creek,  which  crosses  the  east  end  of  the  area,  the  coal 
bed  thins  rapidly  to  the  south  and  becomes  shaly  at  a point  near  the 


« Weed,  W.  H.,  Bull.  Geol.  Soc.  America,  vol.  3,  1892,  pp.  301-330, 


52  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

mouth  of  Otter  Creek.  Toward  the  north  the  same  is  true,  although 
in  a less  marked  degree,  to  a point  a short  distance  above  the  mouth 
of  Little  Belt  Creek,  where  the  dip  of  the  rock  carries  the.  coal  beneath 
the  river.  The  bed  is  thickest  in  the  vicinity  of  Armington  and  Belt, 
and  in  either  direction  from  this  zone  there  is  a perceptible  thinning. 
The  eastern  border  of  the  workable  coal  area  can  not  be  definitely 
determined,  for  the  coal  east  of  Belt  is  not  exposed,  but  along  the 
lower  part  of  Otter  Creek  the  workable  bed  thins  rapidly  to  the  east, 
a condition  which  is  believed  to  indicate  that  the  eastern  limit  of  the 
workable  coal  should  be  placed  not  more  than  2 miles  east  of  Belt 
Creek. 

According  to  exposures  along  Sand  Coulee,  the  coal  bed  thins  to 
the  south,  near  the  northern  line  of  T.  18  N. ; and  to  the  north  in  sec. 
2,  T.  19  N.,  R.  4 E.,  it  is  only  a few  inches  thick.  The  bed  reaches 
its  maximum  thickness  between  Straight  and  Giffen  coulees,  where 
the  larger  coal  mines  are  located.  In  the  Smith  River  valley,  near 
the  mouth  of  Hound  Creek,  the  coal  bed  has  a good  workable  thick- 
ness, which  it  maintains  toward  the  north,  possibly  with  slight  thin- 
ning as  far  as  sec.  1,  T.  17  N.,  R.  2 E.,  where  the  bed  passes  beneath 
the  river.  How  far  workable  coal  extends  northwest  of  this  point 
is  not  known,  but  it  seems  probable  that  it  continues  for  at  least  2 or 
3 miles.  The  southern  limit  of  the  Sand  Coulee  area  was  not  ascer- 
tained, for  the  investigation  did  not  extend  beyond  the  southern 
border  of  T.  17  N.,  where  a local  fold  of  the  strata  carries  the  coal 
beneath  the  river;  as  it  is  of  workable  thickness  at  the  southernmost 
point  examined,  it  may  possibly  continue  thus  for  some  distance. 

On  upper  Ming  Coulee  the  coal  bed  has  a maximum  thickness  of  8 
feet,  but  2 miles  farther  up  this  stream  the  dips  are  steep  and  the 
bed  occupies  the  summits  of  high  hills,  where  the  covering  is  thin 
and  the  coal  more  or  less  shaly.  Along  the  north  side  of  the  wagon 
road  leading  from  Ming  Coulee  to  Rocky  Coulee  the  coal  bed  has 
been  prospected  at  many  places,  especially  in  secs.  21,  22,  and  14, 
T.  17  N.,  R.  3 E.  In  most  of  these  prospects  the  coal  horizon  was 
marked  by  only  a few  inches  of  carbonaceous  shale,  which  locally 
thickens  and  in  one  place  becomes  nearly  workable.  From  these 
observations  it  is  believed  that  the  southern  limit  of  the  Sand  Coulee 
area  in  this  part  of  the  field  lies  some  distance  north  of  the  wagon 
road.  The  limits  of  this  area  as  based  on  the  evidence  are  shown  on 
PL  II. 

CHARACTER  AND  THICKNESS  OF  COAL  BED. 

The  Sand  Coulee  area  is  underlain  by  one  coal  bed  of  commercial 
importance.  In  this  bed,  consisting  of  coal  interbedded  with  layers 
of  bone,  shale,  and  clay,  the  coal  content  ranges  in  thickness  from  6 
to  14  feet  in  different  parts  of  the  field.  At  Belt,  in  the  northeast 
end  of  the  area,  where  the  bed  has  been  opened  at  many  places,  the 


COAL. 


53 


average  thickness  of  twenty-six  measured  sections  is  4 feet  7 inches. 
At  Sand  Coulee  fourteen  measured  sections  give  an  average  thickness 
of  8 feet  7 inches,  and  along  Smith  River,  where  fewer  openings  have 
been  made,  an  average  of  five  sections  shows  a total  thickness  of  7 
feet  6 inches  of  coal.  In  the  vicinity  of  Belt  the  coal  is  divided  into 
three  distinct  benches — a lower,  middle,  and  upper.  The  lower  and 
upper  benches  are  in  many  places  about  equal  in  thickness,  the  middle 
bench  being  considerably  thinner.  (See  PL  VIII.) 

At  Sand  Coulee  the  coal  bed  generally  occurs  in  two  principal 
benches,  the  upper  being  much  thicker  than  the  lower.  (See  PI.  X.) 
Above  the  uppermost  bench  worked,  however,  there  are  in  some 
places,  notably  in  the  Smith  River  district,  two  higher  layers  of  coal 
which  have  a maximum  measured  thickness  of  5 feet  8 inches.  From 
a comparison  of  the  average  thickness,  number,  and  order  of  the 
various  coal  benches  in  the  Belt,  Sand  Coulee,  and  Smith  River 
mining  districts,  it  is  apparent  that  the  coals  of  this  basin  are  of 
broadly  lenticular  character  and  it  seems  probable  that  the  total 
thickness  of  coal  contained  in  the  coal-bearing  zone  is  greatest  in  the 
Sand  Coulee  mining  district. 

Graphic  sections  of  the  coal  in  the  Sand  Coulee,  Otter,  and  Sage 
Creek  areas  are  shown  in  Pis.  X-XII.  In  the  following  discussion  of 
the  coals  of  these  areas  individual  sections  are  referred  to  by  num- 
bers corresponding  to  those  used  on  these  plates. 

DEVELOPMENT. 

Development  of  the  coal  resources  of  the  Great  Falls  coal  field  was 
first  begun  in  the  Sand  Coulee  basin  at  Belt,  where,  in  1876,  a small 
mine  was  opened,  the  coal  being  shipped  overland  to  Fort  Benton, 
a town  situated  near  the  head  of  navigation  on  Missouri  River.  For 
the  first  few  years  the  coal  output  of  this  field  was  small,  but  with 
the  opening  of  mines  at  Sand  Coulee,  on  Smith  River,  which  took 
place  a few  years  later,  the  amount  was  increased.  In  1885  the 
combined  production  of  the  Belt  and  Sand  Coulee  mines  was  1,900 
tons,  of  which  1,200  were  from  the  Belt  mines.  During  the  follow- 
ing year  the  output  of  these  two  localities  amounted  to  only  1,400 
tons,  the  greater  part  being  supplied  by  the  Sand  Coulee  mines.  The 
reports  on  Cascade  County  for  1887  give  a relatively  small  yield,  but 
during  the  following  year,  with  the  completion  of  railroad  facilities 
to  Sand  Coulee,  the  total  coal  production  of  the  region  was  mate- 
rially increased.  From  1888  to  1892  the  annual  coal  output  of  the 
Sand  Coulee  basin  grew  steadily  with  the  improvements  made  in 
the  facilities  for  handling  coal  at  the  Sand  Coulee  mines;  during  1893 
the  total  production  of  the  region  increased  over  100  per  cent.  Since 
1880,  when  the  first  systematic  record  of  the  coal  production  of 
Montana  was  kept,  Cascade  County  has  been  one  of  the  largest  pro- 


54 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


(hieing  counties  in  the  State.  Its  relative  output,  with  respect  to 
that  of  the  State  as  a whole,  is  shown  in  the  following  table: 


Coal  production  of  Montana  and  Cascade  County  from  1880  to  1906,  inclusive,  a 

[Short  tons.] 


Y ear. 

Montana. 

Cascade 

County. 

1880 

224 
5,000 
10, 000 
19, 795 
80, 376 
86, 440 
49, 846 
10, 202 
41,  467 
363, 301 
517,  477 
541, 861 
564, 648 
892,  309 
927, 395 

1881 

1882 

1883 

1884 

1885 

1,900 

1,400 

1886 

1887 

1888 

4,  600 
166, 480 
200,  435 
198, 107 
242, 120 
516,  460 
638, 960 

1889 

1890 

1891 

1892 

1893 

1894 

Year. 

j Montana. 

Cascade 

County. 

1895 

1,504,193 
1, 543, 445 
1,647,882 
1,479,803 
1,496,451 
1,661,775 
1,396,081 
1,560,823 
1,488, 810 
1,358,919 
1,643,832 
1,838,635 

713  877 

1896 

1, 10l|  298 
1, 138, 590 
988, 821 
965,378 
1,123,395 
789, 407 
761, 572 
733  064 

1897 

1898 

1899 

1900 

1901 

1902 

1903 

1904 

599’  158 
826, 026 
991,  417 

1905 

1906 

Total 

22, 730, 990 

12,  702,  465 

« Mineral  Resources  U.  S.,  1880  to  1906,  inclusive,  U.  S.  Geol.  Survey. 


Although  at  the  present  time  coal  prospects  and  small  mines  are 
located  at  many  different  places  throughout  the  Sand  Coulee  area, 
development  is  confined  chiefly  to  three  localities  where  stream  val- 
leys crossing  the  district  cut  and  expose  the  coal-bearing  rocks. 
These  districts  of  principal  development  are  along  Belt  Creek,  Sand 
Coulee,  and  Smith  River. 


BELT  CREEK  MINES. 


GENERAL  STATEMENT. 


Along  Belt  Creek  and  its  tributaries  near  the  town  of  Belt  the  coal 
bed  has  been  extensively  prospected  and  a number  of  mines  are  now 
being  operated.  The  mine  of  the  Anaconda  Copper  Mining  Company 
is  the  largest  in  the  district,  but  there  are  four  smaller  ones  which 
are  worked  continuously,  and  seven  abandoned  mines,  some  of  which 
have  produced  considerable  coal  in  the  past.  Prospecting  has  been 
extensive,  especially  along  Neel  Creek,  on  either  side  of  Belt  Creek, 
and  in  Armington  Coulee.  A number  of  diamond-drill  prospect 
holes  have  been  bored  by  the  larger  companies  on  the  plateau  west  of 
Belt  Creek  in  order  to  determine  the  character  of  the  coal  bed  under- 
lying their  holdings.  The  location  of  the  mines  are  shown  on  PI.  II; 
sections  of  the  coal  beds  are  shown  on  PI.  VIII. 


MINES  OPERATED. 

Anaconda  Copper  Mining ' Company  mine. — The  mine  owned  and 
operated  by  the  Anaconda  Copper  Mining  Company,  of  Anaconda, 
Mont.,  is  located  on  the  west  side  of  Belt  Creek,  at  the  town  of  Belt. 
(See  PI.  IX.)  The  principal  coal  holdings  of  the  company,  which 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  356  PL.  VIII 


BELT  CREEK  DISTRICT 


Boston  & Montana 


Richardson  mine  mine,  lOO'from  Schmauch  mine  Millard  mine  Clingan  mine 


24 

Hill  mine 


at  Armington  mouth  of  main  entry  near  Belt 
22' 


at  Belt 


l8’/z  5+2  "t 

[16"  3 | 

12"+46Va"=58V2"  | 


11 

12+2 


8X2 

4" 


8V2"+  64  Vs"-  63 

10 

Anaconda  Ck>pper  ....,, 
Mining  Co.  mine  16  + 61  /z  -7T  /2 


mm  ivz 

1 ggg 

8"+54V2"=62V2" 


12 1/2  61/2"+64"=701/2"  13 

Anaconda  Copper 
Mining  Co.  mine 


11 


14 


17"+  44"=  61" 
12 

Anaconda  Copper 
Mining  Co.  mine 
between  Nos.  18 


n^r  fault  at  end  15  Anaconda  Copper  Room  2,  No .17  Anaconda  Copper  and  19  entnes 

18  of  No.  16  entry  Anaconda  Copper  Mining  Co.  mine  entry,  south  Mining  Co  mine  ““ 

■I  Mining  Co.  mine  end  of  No.  18  — - - 

•iflGI  ..  No.  13  entry,  south  entry 


Herman  & Powell 
mine  near 
Armington 


No.  13  entry,  south 


I 20 


16' 


1 2.3" 


.34' 


12"+58"=70"  8"+72"=S 


35" 


17  "+57"=  74"  11+71=  82 


Anaconda  Copper  Anaconda  Copper 
Mining  Co.  mine  Mining  Co.  mine 
No.  18  entry,  north  No.  9 entry,  south 


16*4" 


3>/2' 


4*4"  I 


7V2"+55"=62V2"  121/2.^65V2. 


SMITH  RIVER  DISTRICT 
65  , 64 

Love  mine  75  from  Love  mine  66 

mouth  of  main  entry  end  of  main  entry  Bickett  mine 


10"  i 


5 

2"B- 

7"+ 58"= 


4"+ 62"=  66" 


Gibson  mine 


8"+86"=93' 


Impure  or 
bony  coal 


14" 


38"+104"=142" 


3"+55"=58" 


Thickness  of  coal  shown  to  right  of  sections  Thickness  of  waste  shown  to  left  of  sections 
Vertical  scale,  1 inch=  5 feet 


SECTIONS  OF  COAL  IN  BELT  CREEK  AND  SMITH  RIVER  DISTRICTS,  MONT. 


COAL. 


55 


comprise  several  acres,  lie  in  secs.  26  and  27,  T.  19  N.,  R.  6 E.  This 
mine  was  first  opened  in  1895,  and  has  been  in  continuous  operation 
since  that  time.  At  present  the  company  employs  a large  force  of 
men  and  produces  a considerable  tonnage.  The  mine,  however,  is 
not  worked  at  its  full  capacity,  the  output  being  controlled  by  the 
requirements  of  the  company’s  plant  at  Anaconda,  a point  to  which 
much  of  the  coal  is  shipped. 

The  bed  at  this  place  has  an  average  thickness  of  6 feet,  including 
partings,  and  occurs  in  three  benches.  The  lowest  bench  is  about  2 
feet  6 inches  thick,  and  is  overlain  by  2 to  4 inches  of  bone,  followed 
by  the  middle  bench,  which  is  usually  about  7 inches  thick.  Above 
this  7-inch  layer  occurs  bone  parting  3 to  8 inches  thick,  followed  by 
a bed  of  coal  1 to  3 feet  thick,  constituting  the  uppermost  bench. 
There  appears  to  be  little  difference  in  the  physical  properties  of  the 
coal  in  the  different  benches.  The  bed  usually  has  a shale  roof  and 
floor  and  lies  nearly  horizontal,  dipping  only  slightly  to  the  north. 
Sulphur  in  the  form  of  pyrite  nodules  occurs  in  all  the  benches.  A 
number  of  graphic  sections  of  the  coal  bed  in  this  mine  are  shown  in 
PI.  VIII. 

The  underground  workings  of  the  mine  are  very  extensive.  The 
main  entry  has  been  driven  for  about  1J  miles  from  the  outcrop,  with 
numerous  side  entries  to  the  north  and  south  one-half  mile  or  more 
in  length.  The  entire  workings  cover  an  area  of  about  600  acres. 
The  coal  is  taken  out  by  the  room-and-pillar  system  and  brought  to 
the  surface  by  cable  haulage.  The  mine  is  provided  with  a double 
entry,  and  ventilation  is  effected  by  a large  fan  located  near  the 
entrance.  Electric  lighting  is  used  only  in  the  main  entries,  and  the 
water  is  removed  by  large  pumps. 

Owing  to  the  large  amount  of  impurities  present  in  the  bed  it  is 
necessary -to  wash  the  machine-mined  coal.  The  method  employed 
is  as  follows:  The  coal  is  carried  from  the  mine  in  pit  cars  having  a 
capacity  ranging  from  2 to  2\  tons  each,  by  means  of  a cable  and 
tail  rope.  A trip  consists  of  48  cars,  which  on  arriving  at  the  mouth 
of  the  mine  are  uncoupled  and  allowed  to  run  one  by  one  down  a 
gravity  incline  from  which  the  car  is  switched  onto  one  of  three 
tipples,  according  to  the  character  of  the  coal  it  contains.  After  the 
cars  are  unloaded  they  are  gathered  again  on  a single  track  and 
returned  to  the  mine. 

The  tipple  over  which  the  hand-mined  coal  is  dumped  is  connected 
directly  by  chute  to  the  railroad  cars  below.  The  two  remaining 
tipples  are  connected  with  a heavy  sharp-toothed  crusher  by  long 
chutes,  which  are  sufficiently  large  to  serve  as  temporary  storage 
bins.  At  the  crusher  all  the  machine-mined  coal  is  reduced  to  a 
small  size.  It  is  then  carried  by  means  of  an  inclined  conveyor  to 
the  top  of  the  washery,  which  consists  of  three  large  washers  and  a 


56  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

number  of  jigs.  The  amount  of  coal  cleaned  at  this  plant  ranges 
from  250  to  300  tons  a day. 

The  large  washer  consists  of  a steel  chamber  in  the  form  of  an 
inverted  cone,  inside  of  which  are  projecting  arms  and  stirring  plates 
revolved  by  a driving  gear  above.  The  water  supply  enters  at  the 
bottom  from  a perforated  pipe.  The  coal  is  introduced  at  the  top 
from  a chute  and  is  kept  in  a continual  state  of  agitation  by  a current 
of  water.  As  it  is  lighter  than  the  impurities,  it  remains  at  the  top 
and  passes  out  through  the  overflow  into  conveyors,  while  the  water 
and  sludge  drain  through  the  hopper  into  a sludge  tank.  The 
impurities  sink  into  a lower  chamber  of  the  washer,  which  is  pro- 
vided with  two  valves,  one  above  and  one  below.  When  this  chamber 
is  filled,  the  upper  valve  is  closed  and  the  lower  opened  to  discharge 
the  refuse.  By  this  process  the  coal  is  cleaned  rapidly,  but  the 
results  on  the  whole  are  not  so  satisfactory  as  those  obtained  by 
the  jigs. 

The  jig  washer  consists  essentially  of  a large  wooden  tank  divided 
into  two  compartments,  one  containing  a screen  on  which  are  placed 
a number  of  small  pieces  of  feldspar,  the  other  provided  with  a piston 
moved  up  and  down  by  means  of  an  eccentric,  imparting  to  the 
water  the  necessary  pulsations.  By  this  means  the  water  is  forced 
up  through  the  screen,  lifting  the  unassorted  material  and  allowing 
it  to  settle  again,  thus  affording  an  opportunity  for  the  products  of 
different  specific  gravity  to  adjust  themselves  according  to  the  law 
of  equally  falling  particles.  The  coal  remains  at  the  top  of  the 
wooden  tank,  the  slate  next  below,  and  the  pyrite  at  the  bottom. 
These  products  of  separation  are  drawn  off  through  gates  placed  at 
proper  heights  in  the  sides  of  the  jig  and  are  carried  away  by  screw 
conveyors — the  coal  to  a large  bin,  where  it  is  allowed  to  drain;  the 
pyrite  to  an  elevator,  where  it  is  rinsed  and  dropped  into  railroad 
cars;  and  the  slate  to  the  waste  pile.  The  water  used  in  the  washery 
is  taken  to  a tank  outside  the  plant,  and  after  the  sediments  which 
it  contains  have  settled  to  the  bottom,  the  clear  water  is  drawn  off 
from  the  top  and  pumped  back  into  the  washer. 

The  iron-pyrite  nodules  removed  by  the  above-described  process 
are  shipped  as  a by-product  to  the  large  smelters  at  Great  Falls, 
where  they  are  used  as  an  additional  fuel  and  flux  in  the  blast- 
furnace charge.  By  this  utilization  the  pyrite  pays  for  its  separation 
from  the  coal. 

Coal  from  the  middle  bench  of  the  Belt  Creek  bed  was  formerly 
coked,  and  100  ovens  having  a capacity  of  3 tons  each  were  built  for 
this  purpose.  It  was  found,  however,  that  the  bench  of  coking  coal 
was  too  thin  to  pay  for  its  separation  from  the  other  varieties  of  coal, 
and  consequently  the  coke  ovens  are  not  now  used.  A view  of  the 
Anaconda  Copper  Mining  Company’s  plant  at  Belt  is  shown  in  PI.  IX. 


ANACONDA  COPPER  MINING  COMPANY'S  COAL  PLANT  AT  BELT,  MONT. 


COAL. 


57 


Schmauch  mine. — The  Schmauch  mine,  situated  on  the  east  side 
of  Belt  Creek  at  Belt,  nearly  opposite  the  Anaconda  Copper  Mining 
Company’s  mine,  is  probably  the  'largest  of  the  smaller  openings. 
This  mine  is  worked  continuously  by  a few  men,  but  it  has  only  a 
small  output,  which  is  sold  to  ranchmen  in  the  vicinity  of  Belt.  The 
entry  extends  several  hundred  feet  from  the  outcrop,  but  the  exact 
length  could  not  be  measured  owing  to  cavings  in  the  mine.  The 
bed  lies  nearly  horizontal,  dipping  slightly  to  the  north.  A represen- 
tative section  shows  a thickness  of  about  6§  feet,  consisting  of  three 
benches.  The  lowest  is  28  inches  thick,  containing  a bone  parting 
3^  inches  thick  12  J inches  above  the  base.  Above  this  bench  is  a 
4-inch  layer  of  bone,  followed  by  3 inches  of  coal,  constituting  the 
middle  bench.  This  is  overlain  by  8 J inches  of  bone,  which  is  followed 
in  ascending  order  by  a bed  of  coal  34  inches  thick — the  top  bench  (5). 
The  occurrence  of  a bony  layer  in  the  lower  bench  of  coal  is  unusual 
in  this  district. 

Millard  mine. — The  Millard  mine  is  situated  a few  hundred  yards 
south  of  the  Schmauch  mine,  on  the  same  side  of  Belt  Creek.  Here 
an  entry  has  been  driven  about  700  feet  from  the  outcrop,  with  side 
entries  leading  to  the  north  and  south.  The  bed  is  about  6 feet 
thick,  containing  partings  *which  separate  the  coal  into  three  benches, 
the  lower  28  inches,  the  middle  6 inches,  and  the  top  30  inches  (7). 
The  lowest  bench  is  regarded  by  the  miners  as  containing  the  best 
quality  of  coal,  that  of  the  middle  and  uppermost  benches  being  of  a 
slightly  inferior  grade.  The  Millard  mine  has  a very  small  output, 
and  most  of  the  coal  is  sold  in  the  town  of  Belt. 

Richardson  mine. — On  the  east  side  of  Belt  Creek  at  Armington  is 
another  mine,  owned  by  Matthew  Richardson,  which  is  worked 
during  the  winter  months.  The  coal  here  exhibits  the  usual  thick- 
ness of  about  4J  feet,  including  partings.  The  three  characteristic 
benches  are  represented— a lower,  middle,  and  upper.  The  upper- 
most has  a thickness  of  1 foot  10  inches,  the  middle  and  lowest  are 
8J  and  16  inches  thick,  respectively.  A section  of  this  bed  is  shown 
in  PL  VIII,  No.  26.  The  coal  is  bright  and  clean  looking,  and  in 
composition  does  not  differ  materially  from  the  average  coal  found 
near  Belt.  The  output  of  the  mine,  which  is  small,  is  sold  in  Arm- 
ington and  to  ranchmen  along  Belt  Creek  valley. 

Orr  mine. — About  1 J miles  north  of  Belt,  on  the  east  side  of  Belt 
Creek,  there  is  a mining  property  owned  by  the  Orr  Brothers,  which 
is  worked  to  a certain  extent,  chiefly  in  the  way  of  development. 
A main  entry  has  been  driven  700  feet  from  the  outcrop,  with  side 
entries  of  considerable  length. 

The  coal  appears  to  be  of  inferior  quality  and  the  large  amount 
of  material  taken  out  in  excavating  the  entries  could  not  be  placed 
on  the  market.  The  coal  is  dull  or  lusterless  and  is  not  firmly  bedded. 


58  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

An  analysis  of  an  air-dried  sample  shows  about  44  per  cent  fixed 
carbon,  21  per  cent  volatile  matter,  28  per  cent  ash,  and  a small 
amount  of  sulphur.  A representative  section  of  the  mine  shows 
five  benches  of  coal,  with  an  aggregate  thickness  of  4 feet  5 inches. 
The  lowest  bench  is  10  inches  thick,  followed  by  3 inches  of  bone, 
which  in  turn  is  overlain  by  10  inches  of  coal.  Above  this  coal  is  a 
12-inch  layer  of  bone  overlain  by  7 inches  of  coal  of  a rather  inferior 
variety.  Over  this  coal  is  10  inches  of  bone  followed  by  22  inches 
of  coal,  constituting  the  uppermost  bench  of  the  bed.  A comparison 
of  this  coal  bed  with  those  in  the  Schmauch  and  Millard  mines  indi- 
cates that  partings  have  developed  in  both  the  lower  and  upper  coal 
benches. 

ABANDONED  MINES. 

The  remaining  small  mines  of  the  Belt  district  are  the  Hill,  Buzzo 
or  Hill,  Boston  and  Montana,  Herman  & Powell,  Watson,  Brady, 
and  American  Smelting  and  Refining  Company. 

Hill  mine. — An  abandoned  mine,  said  to  be  now  owned  by  J.  J. 
Hill,  is  located  on  the  west  side  of  Belt  Creek  at  Armington.  A large 
entry  has  been  excavated,  and,  to  judge  from  the  size  of  the  dump, 
considerable  coal  was  taken  out.  A section  of  the  bed  shows  3 feet  2 
inches  of  coal,  not  including  three  layers  of  bony  coal  which  occur 
near  the  middle  (24).  The  coal  is  apparently  of  good  quality,  but 
contains  the  usual  amount  of  sulphur  in  the  form  of  iron-pyrite 
nodules.  The  uppermost  bench  is  characterized  by  joint  planes  run- 
ning in  opposite  directions,  separating  the  coal  into  small  cubical 
blocks. 

Buzzo  or  Hill  mine. — About  one-fourth  mile  south  of  the  aban- 
doned Hill  mine,  on  the  same  side  of  Belt  Creek,  there  is  another 
opening  known  as  the  Buzzo  mine,  also  owned  by  J.  J.  Hill.  This 
mine  is  more  or  less  caved  at  the  mouth  of  the  entry,  but  the  general 
succession  of  the  members  in  the  coal  bed  was  obtained.  Three 
benches  of  coal  are  present,  the  lowest  14  inches,  the  middle,  which 
is  very  impure,  5|  inches,  and  the  uppermost  30  inches  thick  (22). 
The  coal  appears  to  be  of  good  quality  in  the  uppermost  bench,  but 
that  found  in  the  middle  bench  is  inferior.  No  analysis  was  made. 
The  entry  is  said  to  be  500  feet  long,  but  as  the  mine  was  flooded  it 
was  impossible  to  examine  in  detail  the  underground  workings.  The 
mine  has  a sandstone  roof  and  a clay  floor. 

Boston  and  Montana  mine. — The  Boston  and  Montana  mine,  located 
about  500  yards  south  of  Orr  Brothers’  mine,  in  the  SE.  J sec.  23,  T. 
19  N.,  R.  6 E.,  contains  a bed  of  coal  similar  in  many  respects  to  that 
found  in  the  Orr  mine.  It  has  a sandstone  roof  and  shale  floor.  A 
graphic  section  of  the  bed  is  given  in  PI.  VIII,  No.  2.  The  three 
benches  have  an  aggregate  thickness  of  54  J inches.  The  lowest  con- 
tains a layer  of  bone,  or  bony  coal,  12  J inches  above  the  base.  This 


COAL. 


59 


bench  is  overlain  by  5|  inches  of  bone,  which  is  followed  by  the  mid- 
dle bench  of  coal,  3 inches  thick.  Above  the  middle  bench  there  is  a 
thin  bony  parting  underlying  28  inches  of  impure  coal,  the  top  bench 
of  the  bed.  A comparison  of  the  sections  at  the  Orr  and  at  the 
Boston  and  Montana  mine  appears  to  indicate  that  the  quality  of 
the  coal  becomes  better  to  the  south. 

Herman  Ac  Powell  mine. — About  300  yards  north  of  the  Richard- 
son mine,  on  the  eastern  side  of  Belt  Creek  at  Armington,  there  is  an 
abandoned  opening  known  as  the  Herman  & Powell  mine.  Two 
entries  75  feet  apart  have  been  excavated  on  the  bed.  The  south 
entry  is  250  feet  long,  extending  in  a southeasterly  direction,  but  has 
no  side  entries.  A section  of  the  coal  bed  in  this  entry  shows  4 feet 
of  coal  separated  into  three  benches,  the  lowest  18  inches,  the  middle 
11  inches,  and  the  uppermost  19  inches  thick  (18).  The  mine  has  a 
slate  roof  and  a clay  floor.  The  north  entry  is  350  feet  long  and  runs 
in  a northeast  direction.  It  has  one  entry  on  the  southeast,  which 
branches  from  the  main  tunnel  75  feet  from  its  mouth.  A section  of 
the  bed  in  this  entry  shows  a thickness  of  54  \ inches  divided  into 
lower,  middle,  and  upper  benches,  measuring  16J,  11,  and  27  inches, 
respectively.  The  roof  is  dark-colored  shale  and  the  floor  clay.  This 
mine  has  not  been  operated  for  several  years,  but  according  to  reports 
considerable  coal  was  formerly  taken  out. 

Watson  mine. — About  one-fourth  mile  south  of  the  Richardson 
mine  a tributary  canyon  known  as  Armington  Coulee  enters  Belt 
Creek  valley.  On  both  sides  of  this  coulee  the  coal  bed  is  exposed, 
and  several  openings  have  been  made.  The  largest  on  the  south  side 
of  the  coulee  is  known  as  the  Watson  mine.  Here  an  entry  has  been 
excavated  for  a distance  of  160  feet,  exposing  a bed  of  coal,  including 
partings,  5 feet  1J  inches  thick.  Of  this  amount  4 feet  1 inch  con- 
sists of  coal,  the  remainder  of  dark-colored  bony  material.  Three 
benches  are  recognized,  the  lowest  13  inches  thick,  the  middle  13^ 
inches,  and  the  uppermost  22^  inches.  The  middle  bench  appears  to 
be  of  an  inferior  quality,  although  no  analysis  has  been  made.  The 
lower  bench  contains  a large  amount  of  sulphur  in  the  usual  form. 
The  bed  has  a slate  roof  and  shale  floor. 

Brady  mine. — On  the  north  side  of  Armington  Coulee,  directly  oppo- 
site the  Watson  mine,  there  is  an  abandoned  opening  known  as  the 
Brady  mine.  The  entry  at  this  place  extends  150  feet  from  the  out- 
crop, with  one  room  on  either  side.  The  coal  bed  has  a total  thick- 
ness of  55 \ inches.  The  coal  of  the  lower  bench  is  bright  looking, 
but  contains  much  sulphur  in  nodular  form.  The  coal  in  the  upper 
part  of  the  top  bench  has  a dull  appearance  and  is  probably  of  infe- 
rior grade. 

American  Smelting  and  Refining  Company  mine. — On  the  west 
side  of  the  main  road  between  Armington  and  Belt,  near  the  Belt 


60  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

cemetery,  there  is  an  abandoned  entry  which  was  excavated  by  the 
American  Smelting  and  Refining  Company.  This  entry  is  well  tim- 
bered, and  the  indications  are  that  plans  were  laid  for  extensive 
development.  The  property  is  now  abandoned,  and  the  entry  is 
caved  so  that  it  could  not  be  examined  for  more  than  a few  feet  from 
the  mouth.  No  information  was  obtained  regarding  the  quality  of 
the  coal. 

PROSPECTS. 

Entry  prospects. — Considerable  prospecting  has  been  carried  on  in 
Belt  and  vicinity.  Along  Neel  Creek,  one  of  the  principal  tributaries 
of  Belt  Creek  from  the  west,  coal  prospects  can  be  seen  at  short  inter- 
vals on  either  side  of  the  canyon.  Few  of  these  prospects  extend 
more  than  a few  feet  from  the  outcrop  and  they  appear  to  have  been 
opened  more  to  determine  the  thickness  of  the  coal  bed  than  with  the 
intention  of  developing  a mine.  One  of  the  largest  of  these  prospects, 
which  may  be  regarded  as  a small  mine,  is  owned  by  E.  R.  Clingan  and 
is  located  in  sec.  2,  T.  18  N.,  R.  6 E.  A section  of  the  bed  at  this 
place  shows  54  J inches  of  coal,  excluding  partings.  The  three  charac- 
teristic benches  are  present,  the  lowest  having  a thickness  of  24 
inches,  the  middle  of  7J  inches,  and  the  uppermost  of  23  inches. 

Diamond-drill  prospects. — In  addition  to  the  above  prospecting, 
more  or  less  diamond-drill  boring  has  been  done  on  the  high  plateau 
west  of  Belt  Creek,  in  order  to  ascertain  the  thickness  of  the  coal  beds 
in  different  parts  of  property  owned  by  large  mining  companies.  No 
logs  of  these  borings  were  obtained. 

SAND  COULEE  MINES. 

GENERAL  STATEMENT. 

Three  large  coal  companies  are  now  operating  along  Sand  Coulee 
and  its  tributary  canyons  in  the  vicinity  of  Stockett.  These  are  the 
Cottonwood  Coal  Company  at  Stockett,  and  the  Nelson  and  Gerber 
coal  companies  at  the  town  of  Sand  Coulee.  In  addition  there  are  a 
number  of  prominent  individual  producers;  those  deserving  especial 
mention  are  the  Mount  Oregon  Coal  Company  and  the  owners  of  the 
Dahn,  Brown,  and  Stainsby  mines.  This  locality  was  the  second 
to  receive  attention  in  the  development  of  the  coal  resources  of  the 
Great  Falls  field,  and  at  present  is  the  largest  producing  district  of  the 
entire  field  and  one  of  the  largest  in  the  State.  Branch  railroad 
lines  connect  Stockett  and  Sand  Coulee  with  the  Neihart  branch  of 
the  Great  Northern  Railway  at  Gerber  station,  and  a large  amount 
of  coal  is  shipped  from  these  towns  to  Great  Falls  and  also  some  to 
more  distant  points  along  the  Great  Northern  main  line  both  to  the 
east  and  west.  The  location  of  the  mines  is  shown  on  PI.  II;  sections 
of  the  coal  beds  are  shown  on  PI.  X. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  356  PL.  X 


55 

Gerber  mine 


47 


54 

48  46  57  .59  Dahn’s  mine 

end  of  north-  Gerber  mine  Gerber  mine  Gerber  mine  Stainsby  mine  Stainsby  mine  100'from  mouth 
east  entry  Room  No.  3 Room  No.  1 Room  No.  1 Room  No.  1.  east  end  of  main  entry  of  main  entry 


42" 


5 Zz 


Nelson  No.  2 
mine 


6 +109  =115 


10‘/a"+143V2" 
= 154" 


51 

Nelson  mine 
No.l  Butt  entry 
off  No.  5 south 


52" 


62 

Cottonwood  Coal 
Co., No.  12  Butt 
off  No.  2 south 

10" 


6"00j 

H -1”  io" 

6"+73"=79" 


7"! 


36"+30"=66" 


16  V2" 


10"+ 108"=  118"  7 ,,+  109V2 " - 1 16 V2 " 


61  60  56 

Cottonwood  Coal  Cottonwood  Coal  Rrnwn  mino 
C0..N0.5  Butt,  off  Co., Room  No.  12  _ ™ 

No.  2 north  off  No.  2 south  3 


72" 


76 

Mount  Oregon 
Coal  Co.,mine 


2V2" 


'167  =nol/s' 


Sarzin  mine 
hear  Stockett 


2l"+ 


Prospect  3 miles 
SW.  of  Stockett 


13" 


13"  i 


m. 

3" 

2" 

17" 


27" 


38" 


2" 


17"+ 120"=  137"  6"+90"=96"  6"+91"=97"  18"+  85"=  103"  3"+  93"=  %"  S0V2"+  78"=  I28V2"  66+"+ 84"=  150' 


Bone 


Impure  or 
bony  coal 


Clay 


Thickness  of  coal  shown  to  right  of  sections  Thickness  of  waste  shown  to  left  of  sections 
Vertical  scale,  1 inch=5  feet 


SECTIONS  OF  COAL  BED  IN  SAND  COULEE  DISTRICT,  MONTANA. 


COAL. 


61 


MINES  OPERATED. 

Cottonwood  Coal  Company  mine. — The  mine  operated  by  the  Cot- 
tonwood Coal  Company,  which  is  owned  by  the  Great  Northern  Rail- 
way, is  located  at  Stockett,  where  the  company  has  extensive  hold- 
ings. Five  mines  have  been  opened  since  1898 — Nos.  1,  2,  and  3 in 
1890;  No.  4 in  1900;  and  No.  5 in  1903.  All  are  in  sec.  36,  T.  19  N., 
R.  4 E.,  mine  No.  1 in  the  eastern  part,  No.  2 in  the  SE.  \ SE.  1, 
No.  3 in  the  NE.  \ SW.  No.  4 in  the  NW.  1,  and  No.  5 in  the 
NW.  \ NW.  i.  This  company  has  carried  on  extensive  mining 
operations  from  the  opening  of  the  first  mine  in  1898.  At  present 
Nos.  1,  2,  3,  and  4 are  abandoned.  The  thickness  of  the  coal  bed 
worked  in  mine  No.  5 (PL  XI,  A)  is  from  5 to  10  feet,  not  including 
partings.  Four  benches  of  coal  are  present  in  this  mine,  the  lowest 
having  a thickness  of  15  inches,  the  next  higher  73  inches,  the  third 
22  inches,  and  the  fourth  and  top  bench  10  inches.  Only  the  first 
and  .second  benches,  however,  are  mined.  The  bed  worked  has  a 
bone  roof  and  clay  floor.  It  lies  nearly  horizontal,  dipping  slightly 
to  the  north.  A graphic  section  showing  the  thickness  of  the 
benches  and  bone  partings  is  given  in  PL  X,  No.  62.  The  coal  con- 
tains sulphur  in  characteristic  nodular  form. 

The  Cottonwood  Coal  Company’s  mine  has  probably  the  best- 
equipped  plant  in  the  Great  Falls  coal  field.  It  is  provided  with 
modern  appliances  for  furnishing  air,  light,  and  water,  both  to  the 
plant  and  to  the  underground  workings.  The  impurities  found  in 
the  different  benches  of  the  coal  bed  are  sufficient  to  make  it  neces- 
sary to  clean  the  coal  before  it  can  be  placed  on  the  market,  and  this 
is  done  by  a dry  process  which  separates  the  sulphur  nodules  and 
the  bone  from  the  coal. 

The  coal  is  carried  from  the  mine  in  pit  cars  of  a capacity  averaging 
about  1J  tons.  After  being  weighed  on  an  automatic  scale  it  is 
dumped  by  a cross-over  tipple  above  a bar  screen,  with  spaces 
between  the  bars  2 inches  wide.  This  screen  separates  out  the  smaller 
pieces  of  coal,  which  constitute  about  30  per  cent  of  the  total,  allow- 
ing them  to  fall  on  a shaking  screen  having  1-inch  round  perforations. 
The  slack  passes  through  the  screen  and  is  loaded  directly  into  rail- 
road cars  or  taken  to  the  boiler  room  by  means  of  a wire-rope  con- 
veyor. The  coal  that  passes  over  the  shaking  screen  slides  into  a 
hopper  from  which  it  is  fed  into  an  elevator  that  carries  it  to  the  top 
of  the  building. 

The  coal  that  passes  over  the  bar  screen  falls  upon  a traveling  belt  4 
feet  6 inches  wide  and  26  feet  long.  Men  stationed  on  either  side  remove 
from  this  belt  any  large  pieces  of  slate  or  other  foreign  matter  such  as 
machine  picks,  car  couplings,  or  sprags,  and  throw  them  into  a rock 
elevator.  The  belt  is  operated  by  a clutch,  so  that  in  case  a large 
quantity  of  impurities  appear  it  can  be  thrown  out  of  gear,  and  all 


62  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

the  impurities  can  be  removed  before  the  coal  goes  on.  The  belt  de- 
livers the  coal  to  rollers,  which  reduce  it  to  a size  not  exceeding  4 
inches  in  largest  dimension.  It  is  necessary  to  reduce  the  coal  to  this 
size  in  order  to  detect  and  remove  the  sulphur  balls  present.  The 
rollers  are  of  removable-tooth  style,  36  inches  in  diameter,  48  inches 
wide,  and  revolve  75  times  per  minute. 

From  the  rollers  the  coal  is  elevated  by  a continuous  elevator  hav- 
ing buckets  with  a capacity  of  110  pounds  of  coal  when  level  full, 
operated  at  a speed  equivalent  to  200  tons  per  hour.  The  capacity 
of  the  fine-coal  elevator  is  90  tons  per  hour,  giving  a combined  elevat- 
ing capacity  of  290  tons  per  hour,  or  2,900  tons  per  day  of  ten  hours, 
an  amount  which,  added  to  the  slack  separated  out  by  the  shaking 
screen,  gives  a total  capacity  of  3,200  tons  per  day. 

The  coal  raised  by  the  elevators  is  evenly  divided  over  an  inclined 
shaking  screen  5 feet  wide  and  46  feet  long,  whose  plates  have  1,  1J-, 
2,  2J,  and  3 inch  round  perforations  which  separate  the  coal  into 
slack,  pea,  nut,  stove,  egg,  and  broken  sizes. 

The  slack  resulting  from  the  breakage  of  the  coal  is  clean,  and,  not 
needing  any  further  preparation,  it  descends  through  a hopper  to  the 
top  strand  of  a conveyor,  which  carries  it  directly  to  the  mixed-coal 
bin.  The  other  sizes  are  fed  by  means  of  other  hoppers  into  spiral 
separators  which  separate  out  the  greater  part  of  the  impurities  by 
means  of  centrifugal  force  and  gravity.  These  impurities  pass  either 
to  the  lower  strand  of  the  conveyor,  being  taken  thence  to  the  rock 
elevator,  or  from  one  set  of  spirals  to  the  bins  by  means  of  chutes, 
which  gives  an  opportunity  to  repick  the  refuse  by  hand  and  save  any 
coal  that  may  still  remain.  The  refuse  is  finally  loaded  into  railroad 
cars  and  used  for  the  purpose  of  widening  banks  along  the  railroad. 

The  coal  from  the  spirals  drops  onto  two  picking  bands  4 feet  wide 
and  50  feet  long,  which  convey  it  to  the  mixed-coal  bin  and  give  an 
opportunity  to  pick  out  by  hand  any  impurities  not  already  removed. 
From  one  set  of  the  spirals  inclined  chutes  carry  the  coal  into  bins  for 
loading  straight  sizes,  any  remaining  impurities  being  removed  by 
hand  while  the  material  is  on  the  chutes. 

On  account  of  the  slight  difference  in  specific  gravity  of  coal  and 
hone,  the  spirals  are  adjusted  so  as  to  retain  only  the  slate  and  flat 
sulphur  balls,  leaving  the  bone  to  be  removed  by  hand.  The  round 
sulphur  balls,  which  on  account  of  their  shape  are  the  first  to  leave 
the  spirals  and  go  with  the  coal,  also  have  to  be  removed  by  hand. 

The  rock  elevator,  having  continuous  buckets  12  by  30  inches  in 
size,  elevates  the  impurities  into  a bin,  from  which  they  are  loaded 
into  a 6-ton  car  and  hoisted  by  a pair  of  gear-tailed  rope  engines  with 
10  by  18  inch  cylinders  to  the  top  of  the  adjoining  hill  and  dumped 
automatically. 


U.  S.  GEOLOGICAL  SURVEY  BULLETIN  NO.  356  PL.  XI 


A.  COTTONWOOD  COAL  COMPANY’S  MINE  NO.  5,  NEAR  STOCKETT,  MONT. 


B.  NELSON  COAL  MINE  AND  PLANT  AT  SAND  COULEE.  MONT. 


COAL. 


63 


The  machinery  of  the  entire  plant  is  driven  by  a double  engine  with 
13  by  18  inch  cylinders,  running  150  revolutions  per  minute. 

The  percentage  of  refuse  in  the  various  sizes  after  being  treated  in 
the  above-described  process  is  stated  below: 

Refuse  remaining  in  coal  at  Cottonwood  Coal  Company’ s mine , Stoclcett,  Mont. 

Per  cent. 


Pea 4 

Nut 3 

Stove 3 

Egg 2 

Broken 1 

Mixed 2.  5 


Of  2,000  tons  of  mine  product  daily  dumped  into  the  breakers,  200 
tons  of  the  various  impurities  are  removed,  and  these  impurities  do 
not  contain  on  an  average  over  1 per  cent  of  coal. 

For  greater  detail  concerning  the  breaker  used  at  this  plant, 
including  diagrams,  the  reader  is  referred  to  a report  by  Lewis  Stockett,® 
of  Stockett. 

Nelson  mines. — The  Nelson  mines,  the  oldest  operated  in  the  Sand 
Coulee  basin,  are  located  at  the  town  of  Sand  Coulee  (PI.  XI,  B). 
There  are  two  mines;  No.  1 is  situated  on  the  east  side  of  Sand  Coulee, 
and  No.  2 is  on  the  west  side,  a short  distance  below  the  town.  Mine 
No.  2 was  first  opened  by  Charles  Locery  in  1905  and  was  later  sold 
to  the  Nelson-Jenks  Coal  Company.  It  is  not  being  worked  at  the 
present  time.  Mine  No.  1 was  extensively  worked  by  the  Cotton- 
wood Coal  Company  before  that  concern  moved  to  its  present  loca- 
tion at  Stockett.  Operations  were  begun  by  the  Nelson  Coal  Com- 
pany at  this  mine  in  1903,  and  since  then  the  property  has  been 
worked  continuously.  The  main  entry  has  been  driven  in  an  easterly 
direction  to  a distance  of  about  3,000  feet  from  the  outcrop,  and  the 
total  acreage  of  the  underground  workings  is  considerable.  The  coal- 
bearing rocks  at  this  mine  are  locally  disturbed,  the  miners  having 
encountered  numerous  rolls;  and  in  places  the  coal  is  entirely  absent. 
The  bed  ranges  in  thickness  from  6 to  9 feet.  It  lies  nearly  level? 
with  a general  but  low  dip  to  the  north,  and  is  composed  of  benches 
like  those  worked  at  the  Gerber  mine,  described  below.  The  lower 
bench  has  a thickness  of  about  1 foot  6 inches  and  the  upper  of  about 
7 feet  6 inches  (50).  Between  the  two  is  a layer  of  dark-colored  bone 
6 to  10  inches  thick.  The  coal  of  both  benches  is  clear,  firm,  and 
noticeably  free  from  foreign  material.  The  sulphur  is  present  in  the 
usual  form,  but  is  not  abundant.  A layer  of  dark-colored  shale  8 
inches  thick  forms  the  roof.  It  is  overlain  by  another  bench  of  coal 
which  is  not  mined  at  present.  The  floor  consists  of  dark-colored 
shale. 


Stockett,  Lewis,  A bitum.nous  coal  breaker  in  Montana:  Min.  World,  vol.  20,  March  20,  1904. 


64  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

The  company  employs  about  175  men,  who  work  continuously,  and 
in  general  the  plant  is  very  well  equipped  for  handling  coal.  Ventila- 
tion is  furnished  by  a 12-foot  fan,  and  the  water  is  taken  out  by  three 
large  pumps.  The  coal  is  machine  mined,  by  the  pillar  and  block 
system,  and  is  cleaned  and  assorted  into  different  sizes  by  means  of  a 
20-foot  picking  table  and  a 44-foot  shaking  screen.  Horse  haulage 
is  employed. 

Gerber  mine. — One  of  the  three  large  mines  in  the  Sand  Coulee  dis- 
trict is  owned  by  the  Rock  Springs  or  Gerber  Coal  Mining  Company. 
It  is  located  on  the  west  side  of  Straight  Coulee,  a tributary  to  Sand 
Coulee,  about  half  a mile  south  of  the  town  of  Sand  Coulee,  in  the 
NE.  \ sec.  23,  T.  19  N.,  R.  4 E.  The  mine  was  opened  in  1890  and  has 
been  worked  continuously  since  that  time.  A large  force  of  men  is 
employed  and  the  underground  workings  are  extensive.  Though 
slight  local  dips  are  more  or  less  common,  the  coal  bed  lies  nearly 
level,  dipping  only  slightly  to  the  north.  It  is  from  6 to  9 feet  thick, 
including  partings.  It  is  believed  that  the  coal  worked  comprises 
the  lower  part  of  the  coal  bed  as  exposed  in  certain  parts  of  this  mine 
and  at  other  places  in  the  Sand  Coulee  district.  Two  benches  are 
present — a lower,  which  has  a thickness  of  about  2 feet,  overlain  by 
2 to  6 inches  of  dark-colored  bone,  followed  by  an  upper  bench  4 to  7 
feet  thick  (46,  47,  48).  Above  the  upper  bench  worked  there  is  in 
some  places  a coal  bed  38  inches  thick  (55).  The  coal  of  all  benches 
is  firm,  clean-looking,  and  noticeably  free  from  bony  partings.  Sul- 
phur, in  characteristic  nodular  form,  is  present  in  considerable  abun- 
dance. The  roof  consists  of  a strong  dark-colored  shale  and  the  floor 
is  a firm,  compact  clay.  A few  rolls  occur  at  different  places  in  the 
bed,  but  in  general  it  is  not  much  disturbed. 

The  Gerber  Mining  Company  has  a well-equipped  plant,  with  the 
usual  modern  appliances  for  handling  coal.  There  is  considerable 
water  in  the  mine,  a portion  of  which  is  taken  by  steam  pumps  to  a 
reservoir  outside  the  mine,  the  remainder  being  pumped  to  a large 
tank  on  the  hillside,  from  which  the  boilers  are  supplied.  The 
tipple  is  located  about  600  feet  from  the  mouth  of  the  mine  at  the 
end  of  the  railroad.  The  coal  is  all  machine  mined,  the  bed  being 
worked  by  the  room  and  pillar  system.  The  coal  is  fairly  free  from 
impurities,  and  such  as  exist  are  taken  out  by  hand  picking  in  the 
mine  and  screening  at  the  tipple,  no  elaborate  process  being  employed. 
The  haulage  is  effected  by  means  of  horses  and  a small  donkey  engine. 
A 12-foot  fan  furnishes  sufficient  air  to  keep  the  mine  well  ventilated. 
Most  of  the  output  is  shipped  to  points  north,  east,  and  west,  local 
sales  being  small. 

Mount  Oregon  Coal  Company  mine. — The  Mount  Oregon  Coal  Com- 
pany mine,  which  is  the  largest  of  the  smaller  mines  in  the  Sand  Coulee 
district,  is  located  near  the  town  of  Sand  Coulee  in  the  SE.  \ sec.  14, 


COAL. 


65 


T.  19  N.,  R.  4 E.  This  mine  is  at  present  worked  by  Thomas  Mokko, 
and  was  opened  in  the  spring  of  1902.  The  bed  worked  has  a 
thickness  of  about  8 feet.  It  consists  of  two  benches,  a lower  bench 
30  inches  thick,  overlain  by  3 inches  of  clay,  followed  by  63  inches 
of  coal,  constituting  the  upper  bench  (76). 

The  main  entry  extends  several  hundred  feet  from  the  outcrop, 
with  numerous  side  entries.  In  working  the  bed  the  room  and  pillar 
system  is  carried  out.  Sufficient  provision  has  been  made  for  the 
proper  ventilation  of  the  underground  workings  and  the  water  is 
taken  out  by  a gravity  system.  The  haulage  is  effected  by  horses, 
and  a coal  bin  of  20  tons'  capacity  is  located  at  the  mouth  of  the  mine. 
The  impurities  are  removed  by  hand  picking  and  screening.  The 
company  employs  18  men  and  has  a daily  output  of  about  45  tons. 

Dahn  mine. — The  Dahn  mine,  located  at  Sand  Coulee,  in  the  north- 
east corner  of  sec.  13,  T.  19  N.,  R.  4 E.,  is  another  of  the  smaller  mines 
of  this  district.  It  was  first  opened  in  1890,  and  has  been  worked 
intermittently  up  to  the  present  time,  changing  hands  several  times 
in  the  interval.  The  coal  bed  underlies  a hill  covering  about  20 
acres.  Most  of  the  coal  in  this  hill  has  been  worked  out.  At  present 
the  output  is  10  to  15  tons  a day  and  only  a few  men  are  employed, 
but  prior  to  1903  the  mine  was  operated  in  a more  extensive  way,  40 
to  50  men  being  employed,  with  an  output  of  about  100  tons  a day. 

The  coal  is  between  13  and  14  feet  thick.  Three  benches  are 
present;  the  lowest  is  3 feet  thick,  the  middle  7 feet,  and  the  upper- 
most 3 feet  2 inches.  Between  the  lowest  and  the  middle  bench  there 
is  a 2^-inch  layer  of  bone,  and  above  the  middle  bench  a 10-inch 
layer  of  shale  (54).  Only  the  lowest  and  middle  benches  are  worked 
in  the  Dahn  mine.  The  mine  has  a shale  roof  and  floor. 

Brown  mine. — A small  coal  opening  owned  and  operated  by  William 
Brown  is  located  in  the  SW.  f SW.  } sec.  18,  T.  19  N.,  R.  5 E.  The 
main  entry  extends  about  500  feet  from  the  outcrop,  with  two  small 
entries  on  either  side.  The  mine  has  been  worked  for  only  about  two 
years.  Although  the  beds  are  nearly  horizontal,  they  are  consider- 
ably broken  and  disturbed,  making  progress  slow.  The  coal  is  about 
7 feet  thick,  divided  into  three  distinct  benches,  the  lowest  3 inches, 
the  middle  10  inches,  and  the  uppermost  6 feet  (56).  Shale  forms 
the  roof  and  floor.  The  output  is  very  small,  and  operations  are 
carried  on  only  during  the  wunter  months. 

Stainsby  mine. — On  the  west  side  of  Cottonwood  Coulee,  about  2 
miles  belovr  Stockett,  near  the  center  of  sec.  19,  T.  19  N.,  R.  5 E., 
is  a small  mine  owned  by  William  Stainsby.  Two  men  are  employed, 
and  a small  amount  of  coal  is  taken  out.  The  bed  has  a thickness  of 
12  feet,  not  including  partings,  which  are  about  22  inches  thick. 
There  are  four  benches  of  coal  in  all — the  lowest  1 foot  5 inches  thick, 
54937— Bull.  356—09 5 


66 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


the  next  higher  5 feet,  the  next  above  that  2 feet  2 indies,  and  the  top 
bench  3 feet  6 inches  (59).  The  coals  of  the  different  benches  do  not 
appear  to  vary  materially  in  quality,  except  that  the  top  bench  con- 
tains an  unusually  large  amount  of  sulphur  in  the  characteristic 
nodular  form. 

ABANDONED  MINES. 

In  addition  to  the  above-described  mines  there  are  in  the  Sand 
Coulee  district  three  abandoned  openings,  known  as  the  Mitchell, 
McKinsey,  and  Sarzin  mines  (PI.  X,  63).  These  are  all  small  and  of 
minor  importance.  A number  of  diamond-drill  prospect  holes  have 
been  sunk  by  some  of  the  larger  coal  companies  holding  property  in 
the  immediate  vicinity. 

SMITH  RIVER  MINES. 

GENERAL  STATEMENT. 

In  the  bluffs  bordering  Smith  River  and  its  tributaries,  Hound 
Creek  and  Ming  Coulee,  the  coal -bearing  zone  is  exposed  at  many 
places.  Coal  has  been  mined  intermittently  throughout  this  district 
for  more  than  twenty-five  years,  and  within  the  last  decade  consider- 
able prospecting  has  been  done  in  order  to  ascertain  the  extent  of  the 
bed.  Several  small  mines  are  now  operated,  and  there  are  a few 
abandoned  mines  from  which  coal  is  occasionally  taken.  Those 
worked  are  the  Carville,  Gibson,  Patterson,  Bickett,  and  Love  mines, 
which  have  a combined  annual  output  of  only  a few  hundred  tons. 
The  locations  of  the  prospects  and  mines  are  shown  on  PI.  II;  sections 
of  the  coal  beds  are  shown  on  PI.  VIII. 

MINES  OPERATED. 

Carville  mine. — The  Carville  mine,  situated  on  the  west  side  of 
Hound  Creek,  in  the  SW.  J SE.  \ sec.  24,  T.  17  N.,  R.  2 E.,  is  one  of 
the  largest  in  the  Smith  River  district.  Coal  has  been  taken  out  at 
this  place  for  about  seven  years.  The  main  entry  extends  375  feet 
west  from  the  outcrop,  with  a side  entry  to  the  south  75  feet  long  and 
40  feet  wide,  branching  from  the  main  entry  90  feet  from  its  mouth. 
On  the  north  side  of  the  main  entry  there  is  another  side  entry  with 
four  large  rooms.  This  mine  is  not  operated  in  an  extensive  way, 
but  it  is  worked  continuously,  the  total  annual  output  being  about 
1,800  tons.  It  supplies  coal  to  ranchmen  throughout  a considerable 
territory  to  the  south  and  west.  The  bed  mined  is  5 feet  6 inches 
thick  with  no  appreciable  partings.  The  lower  6 inches  of  coal  is 
dull  looking  and  in  places  bony,  but  it  is  firm  and  as  a fuel  gives  good 
satisfaction.  Above  this  bed  there  is  a bright  coal  said  to  be  suitable 
for  blacksmithing,  which  contains  numerous  iron-pyrite  nodules. 
The  thickness  and  character  of  the  bed  remain  relatively  uniform 


COAL. 


67 


throughout  the  workings.  The  rocks  at  this  place  dip  slightly  to  the 
north  and  west  and  are  little  disturbed. 

Gibson  mine. — The  Gibson  mine  is  located  in  the  extreme  south- 
east corner  of  sec.  24,  T.  17  N.,  R.  2 E.,  on  the  east  side  of  Hound 
Creek,  opposite  the  Carville  mine.  It  is  operated  only  during  the 
fall  and  early  winter  months,  and  the  annual  output  is  about  1,200 
tons.  The  bed  worked  is  slightly  thicker  than  that  exposed  in  the 
Carville  mine,  measuring  5 feet  10  inches  (69).  The  upper  2 feet  is  a 
bright,  firm-looking  coal.  Beneath  this  member  is  a dull  bony  coal 
10  inches  thick,  followed  by  46  inches  of  dull-looking  coal  which  is 
said  to  burn  well  and  as  a domestic  fuel  is  in  general  satisfactory.  The 
main  entry  extends  for  about  300  feet  at  right  angles  to  the  face  of 
the  bluff.  It  has  two  large  rooms  on  the  north  and  one  side  entry 
on  the  south  extending  diagonally  from  the  main  entry  to  a distance 
of  about  430  feet.  This  entry  is  cut  across  by  another  side  entry, 
which  leaves  the  main  entry  at  right  angles  near  the  back  end.  The 
rocks  lie  nearly  horizontal,  dipping  slightly  to  the  northwest,  and 
are  not  badly  disturbed.  The  mine  is  worked  by  the  room  and 
pillar  system  and  little  difficulty  is  experienced  with  water. 

Patterson  and  Rice  mines. — The  Patterson  mine  is  situated  high  in 
the  blutfs  on  the  east  side  of  Smith  River,  a short  distance  above  the 
mouth  of  Hound  Creek.  The  first  opening  was  made  in  1903,  and 
the  main  entry  now  extends  to  a distance  of  150  feet.  A short  dis- 
tance to  the  east  is  located  the  Rice  mine,  from  which,  it  is  said,  coal 
was  taken  nearly  twenty-five  years  ago.  The  bed  mined  has  a total 
thickness  of  4 feet  10  inches  (78)  and  the  coal  appears  to  be  of  good 
quality. 

Biclcett  mine. — On  the  north  side  of  Ming  Coulee,  about  1J  miles 
above  the  Eden  creamery,  a small  tonnage  of  coal  is  extracted  from 
the  Bickett  mine.  The  coal  zone  or  bed  is  about  18  feet  thick  and 
dips  at  a small  angle  to  the  northwest.  The  upper  10  feet  does  not 
contain  workable  coal,  but  below  this  there  are  two  benches  of  about 
equal  thickness,  separated  by  8 inches  of  bone  (66).  Freshly  ex- 
posed surfaces  of  both  benches  exhibit  bright,  firm  coal.  The  base 
of  the  lower  bench,  however,  contains  considerable  sulphur  in  nodu- 
lar form.  The  floor  and  roof  of  the  mine  are  composed  of  clay  and 
shale,  respectively. 

Love  mine. — The  Love  mine  consists  of  a small  opening  in  the 
bluffs  on  the  south  side  of  Ming  Coulee  about  one-half  mile  above 
the  Eden  creamery,  in  the  E.  \ SE.  J sec.  31,  T.  18  N.,  R.  4 E. 
It  has  been  worked  in  a desultory  way  for  the  last  ten  years,  but 
only  a small  amount  of  coal  has  been  taken  out  and  the  mine  is  poorly 
developed.  The  coal  bed  is  unusually  thick  at  this  place,  measuring 
over  8 feet,  and  though  the  rocks  are  more  or  less  broken  at  the  sur- 
face, it  is  believed  that  an  entry  driven  some  distance  into  the  hill 


68  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

would  encounter  the  coal  undisturbed.  The  coal  zone  shows  the 
usual  variation,  both  in  number  and  thickness  of  coal  beds.  Four 
different  benches  were  recognized,  of  which  only  the  first  and  second, 
counting  from  the  base,  are  mined.  The  lowest  bench  is  14  inches 
thick.  It  is  underlain  by  bone  containing  thin  streaks  of  coal  and 
resting  on  clay.  Above  the  lowest  bench  of  coal  there  is  1J  feet  of 
bone,  followed  by  3 feet  of  coal  constituting  the  upper  bench  mined. 
This  coal  is  overlain  by  8 inches  of  bone,  forming  the  roof  of  the 
mine.  Above  the  roof  there  are  two  coal  benches,  the  lower  18  inches 
and  the  upper  3 feet  thick;  they  are  separated  by  10  inches  of  bone 
(65). 

PROSPECTS. 

In  addition  to  the  above-described  mines  the  Smith  River  district 
contains  a number  of  prospects,  some  of  which  exhibit  coal  of  work- 
able thickness.  One  opening  of  this  character,  owned  by  Mr.  Hoag, 
is  located  in  the  northwest  corner  of  sec.  31,  T.  17  N.,  R.  3 E.,  and 
there  are  others  in  this  immediate  vicinity.  The  location  of  prospects 
and  mines  in  this  part  of  the  Sand  Coulee  basin  is  shown  on  PI.  II. 

OTTER  CREEK  AREA. 

LOCATION  AND  EXTENT. 

The  Otter  Creek  area,  which  is  located  southwest  of  Geyser,  ex- 
tending along  Otter  Creek  for  a distance  of  about  1 0 miles,  lies  mainly 
in  T.  17  N.,  Rs.  8 and  9 E.,  and  includes  a small  portion  of  T.  16  N., 
R.  9 E.  The  southern  limits  of  the  area  are  definitely  marked  by 
the  outcrop  of  the  coal,  along  which  a sufficient  number  of  prospect 
pits  occur  to  indicate  its  workable  character;  but  to  the  east,  north, 
and  west  the  extent  of  the  coal  can  onl}r  be  inferred  from  a study  of 
a comparatively  small  number  of  exposures.  To  the  east  the  last 
exposure  of  coal  of  workable  thickness  is  found  on  the  east  side  of 
Avoca  Creek,  at  the  Chamber  Brothers  mine.  A quarter  of  a mile 
farther  east,  in  a small  tributary  of  Avoca  Creek,  the  Meredith  pros- 
pect shows  that  the  coal  of  this  horizon  is  not  only  of  less  than  a 
workable  thickness,  but  also  of  inferior  quality.  Still  farther  east, 
in  another  tributary  of  Avoca  Creek,  1J  miles  distant  , prospects  show 
that  only  a few  inches  of  coaly  shale  occur  at  the  coal  horizon.  From 
these  prospects  and  natural  exposures  of  the  coal  to  the  east  it  is 
assumed  that  the  eastern  limit  of  the  Otter  Creek  area  must  lie  some- 
where between  the  Chamber  Brothers  mine  and  the  Meredith  prospect. 

Nor  can  the  northern  extension  of  workable  coal  be  more  than 
approximately  located.  As  previously  stated,  the  coal-bearing  rocks 
of  this  general  vicinity  dip  gently  northeast,  passing  beneath  the 
overlying  Colorado  shale,  and  exposures  are  therefore  few.  At  the 
mouth  of  Williams  Creek,  however,  that  stream  has  cut  sufficiently 


COAL. 


69 


deep  to  expose  the  coal  bed,  which  is  not  of  workable  thickness. 
Northwest  of  this  place,  on  either  side  of  Otter  Creek,  where  the 
coal  is  poorly  exposed,  the  bed  consists  of  only  a few  inches  of  coaly 
shale  containing  thin  streaks  of  coal.  On  the  east  side  of  a small 
tributary  of  Little  Otter  Creek,  about  2 miles  south  of  Mann,  there 
are  two  prospects  which  demonstrate  that  the  coal  horizon  shows 
mainly  impure  coaly  shale.  From  this  evidence  it  seems  highly 
probable  that  coal  of  workable  thickness  does  not  continue  beyond  a 
line  extending  northeastward  from  the  coal  exposures  on  the  ridge 
between  the  Chamber  Brothers  mine  and  the  Meredith  prospect 
nearly  to  the  mouth  of  Williams  Creek,  thence  westward  along  the 
south  side  of  Otter  Creek  nearly  to  Little  Otter  Creek,  thence  south- 
ward to  the  vicinity  of  the  Nullinger  mine.  The  limits  of  the  area 
are  shown  in  PI.  II  ; sections  of  the  coal  beds  are  shown  on  PI.  XII. 

CHARACTER  AND  THICKNESS  OF  COAL  BED. 

The  Otter  Creek  area  is  underlain  by  one  bed  of  coal  which  ranges 
in  thickness,  as  indicated  by  exposures,  from  3 to  6 feet;  the  maxi- 
mum thickness,  however,  in  the  center  of  the  basin  probably  exceeds 
6 feet.  The  coal  generally  occurs  in  two  benches,  although  at  one 
mine  three  distinct  benches  were  observed.  The  maximum  thick- 
ness of  workable  coal  is  4 feet,  as  shown  by  the  section  at  the  Nollar 
mine,  where  it  occurs  in  one  bed  with  no  partings.  At  other  places, 
wherever  two  benches  are  present,  the  lower  is  generally  the  thicker 
and  contains  the  better  coal. 

The  parting  between  the  two  benches  is  commonly  bone.  At  the 
mine  where  three  benches  occur  their  total  thickness  is  2 feet  3 inches. 
It  is  difficult  to  give  an  average  section  of  the  coal  bed  in  the  Otter 
Creek  area,  for  only  one  mine  has  been  opened  which  may  be  regarded 
as  representative  of  the  coal  in  the  central  part.  This  mine,  owned 
by  Mr.  Nollar,  shows  a total  thickness  of  4 feet,  as  above  stated.  It 
is  probable  that  over  a considerable  area  the  coal  retains  this  thick- 
ness, possibhr  increasing  somewhat,  but  throughout  the  marginal 
portions  it  doubtless  becomes  thinner. 

DEVELOPMENT. 

GENERAL  STATEMENT. 

The  coals  of  the  Otter  Creek  area  have  not  been  mined  to  any  con- 
siderable extent.  Though  coal  has  been  taken  out  of  different  open- 
ings for  a number  of  years,  the  area  as  a whole  is  practically  unde- 
veloped. The  Billings  and  Northern  Railroad  now  being  constructed 
will  pass  near  the  northern  limit  of  the  field,  thus  affording  transpor- 
tation facilities.  At  the  present  time  only  three  small  mines  are 
worked — the  Nollar,  Nullinger,  and  Chambers  mines.  Of  these  only 


70  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

the  Nollar  is  of  sufficient  size  to  be  regarded  as  a factor  in  the  pro- 
duction of  coal. 

The  locations  of  mines  and  prospects  in  the  Otter  Creek  area  are 
shown  on  PL  II  ; sections  of  the  coal  bed  are  shown  in  PL  XII. 

MINES  OPERATED. 

Nollar  mine. — The  Nollar  mine  is  situated  at  the  base  of  the  bluffs 
on  the  west  side  of  Otter  Creek  in  the  NW.  \ sec.  29,  T.  17  N.,  R.  9 E. 
The  mine  was  first  opened  in  1902  and  during  the  four  years  of  its 
operation  the  total  output  has  not  exceeded  300  tons.  It  is  not 
worked  continuously,  but  a few  tons  of  coal  are  kept  on  hand  to  sup- 
ply a small  local  trade.  The  coal  occurs  in  what  is  apparently  one 
bench  4 feet  thick  (79),  in  which  no  partings  of  appreciable  thick- 
ness were  observed.  The  coal  is  bright  and  firm,  and  on  close  examina- 
tion shows  fine  banding  on  the  surface.  It  contains  the  characteristic 
sulphur  nodules  found  in  other  portions  of  the  field.  The  entry  ex- 
tends 275  feet  from  the  outcrop  in  a southwesterly  direction.  The 
direction  of  the  main  entry  at  this  place  is  not  at  right  angles  to  the 
dip,  which  here  is  about  due  north,  but  at  a slightly  greater  angle  in 
order  to  make  the  entry  gradually  rise,  thus  obtaining  better  drainage. 
Two  side  entries  extend  at  right  angles  from  the  main  entry,  one 
about  80  feet  and  the  other  about  200  feet  from  the  face.  Each  is  75 
feet  long  and  is  provided  with  rooms  parallel  to  the  main  entiy. 
Opposite  the  first  entry  to  the  south  there  is  a front  entry  leading 
northward  from  the  main  entry;  this  is  provided  with  a large  room 
nearly  50  feet  long.  From  the  end  of  the  second  entry  to  the  south 
there  is  a narrow  cross  entry,  which  extends  parallel  to  the  main 
entry,  past  the  south  end  of  the  first  entr}"  to  the  south  and  thence  to 
the  surface. 

Chamber  Brothers'  mine. — Coal  is  taken  during  the  winter  months 
from  the  Chamber  Brothers’  mine,  which  is  located  in  the  NE.  I of 
sec.  4,  T.  16  N.,  R.  9 E.,  on  the  east  side  of  West  Fork  of  Avoca  Creek. 
This  mine  was  opened  in  1903  and  at  present  has  an  entry  which  ex- 
tends nearly  due  east  for  about  125  feet  from  the  face.  The  coal, 
which  is  2 feet  2 inches  thick,  is  separated  into  two  benches,  the 
lower  14  inches  and  the  upper  12  inches  thick.  Between  the  lower 
and  upper  benches  is  a 4J-inch  bed  of  coaly  material.  Above  the 
upper  bench  there  is  17  inches  of  light  bluish-gray  clay,  forming  the 
roof,  overlain  by  dark  shale  which  contains  thin  streaks  of  coal. 
This  member  is  followed  by  a gray  massive  sandstone.  The  floor  of 
the  mine  consists  of  dark-colored  clay.  A complete  section  is  given 
in  PL  XII,  No.  30. 

Nullinger  mine. — The  Nullinger  coal  mine,  situated  on  the  east  side 
of  a small  tributary  of  Little  Otter  Creek,  in  the  SE.  1 sec.  21,  T.  17  N., 
R.  8 E.,  is  also  a very  small  mine,  at  the  present  time  furnishing  coal 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  356  PL.  XII 


27 

74  Larson  mine 

Nullinger  mine  near  Spion  Kop 


i Yz 


OTTER  CREEK  AREA 

31  33  79  28 

Prospect%mile  south-  Meredith  mine  Nollar  mine  Fisher  mine 

east  of  Meredith  mine  southwest  of  Geyser  southwest  of  Geyser  on  Williams  Cr. 


48" 


l1/2,,+36,  = 37 Vs" 


21"+ 30"=  51'' 


, fH  12" 

15"+ 43"=  58" 


0"+48"=48" 


64  V2"+0"=  64  Vs" 


Chamber  Bros!  mine  Prospect y2  mile  we; 

of  Larson  mine 


south  of  Geyser 
12" 


1V2  pgfpSj 
14"+  26"=  40" 


I 


i6y2" 


1 "+  2OV2" = 21V2  " 


Seman  mine 

Hr" 


34 

Hughes  mine 


SAGE  CREEK  AREA 


42 

Fisher  mine 


43  41 

Prospect  1 mile  north-  Prospect  on  east 


Prospect  on  east 


16" 

2"Sm3" 

"+  43"=  73'' 
45 

Sage  Creek 


near  Willow  Creek  west  of  Fisher  mine  side  of  Barnes  Coulee  side  of  Barnes  Coulee  Schultz  mine  Sheep  Co.  mine 


!22" 

9" 

6" 

12" 

22"+49"=7l" 


12" 


i2"|gg 

1 9 Vs" 
15"+  30V2"=45V^" 


5 

4y2" 


48"+ 15"=  63" 


18"+52V2"=70y2" 


11 

10"  J 

77  y2  "+  20  "=  97  V2" 


Impure  or 
bony  coal 


Shale  with 
lenses  of  coal 


Clay 


Thickness  of  coal  shown  to  right  of  sections  Thickness  of  waste  shown  to  left  of  sections 
Vertical  scale,  1 inch=5  feet 


SECTIONS  OF  COAL  BED  IN  OTTER  CREEK  AND  SAGE  CREEK  AREAS  MONTANA. 


COAL. 


71 


for  only  a few  ranches  near  by.  The  coal  bed  has  a thickness  of  3 feet, 
and  is  separated  by  a 1^-inch  layer  of  bone  into  two  benches  (74). 
It  is  a bright  and  firm-looking  coal,  which  doubtless  warrants  more 
extensive  development.  The  entry  has  a pitch  of  about  60°  and  ex- 
tends for  about  100  feet  from  the  face  in  a northeasterly  direction,  at 
considerably  less  than  a right  angle  to  the  direction  of  the  dip,  which 
is  here  nearly  north. 

ABANDONED  MINES. 

There  are  three  small  abandoned  mines  in  the  Otter  Creek  area,  two 
at  the  mouth  of  Williams  Creek.  The  one  on  the  south  side  of  the 
creek  is  known  as  the  Larson.  On  it  several  openings  have  been  made. 
The  opening  nearest  the  road,  from  which  a sample  was  taken,  has  an 
entry  50  feet  long.  Here  the  total  thickness  of  the  coal  is  28  inches, 
with  an  appreciable  amount  of  foreign  material.  About  200  feet  east 
of  tins  opening  there  is  another  mine  which  is  said  to  extend  150  feet 
into  the  hill.  This  was  flooded,  rendering  it  impossible  to  examine  the 
underground  workings.  About  150  feet  still  farther  east  and  at  a 
slightly  higher  level  there  is  another  opening  with  an  entry  135  feet 
long.  In  excavating  this  entry  a dike  of  intrusive  material  at  60  feet 
from  the  surface,  trending  south-southwest,  was  encountered,  and  the 
remainder  of  the  entry  was  excavated  along  one  side  of  this  dike.  The 
coal  in  this  entry  is  about  2\  feet  thick  and  is  overlain  and  underlain 
by  compact  gray  shale.  A graphic  representation  of  the  section  is 
given  in  PI.  XII,  No.  27. 

About  500  feet  farther  east  on  the  same  side  of  Williams  Creek 
another  small  opening  exhibits  a coal  bed  similar  to  the  one  just  de- 
scribed. 

North  of  Williams  Creek,  at  the  mouth,  is  the  Fisher  mine,  in  which 
the  coal  is  22  inches  thick.  The  bed  is  overlain  by  15  inches  of  bone, 
followed  by  6 inches  of  coaly  shale,  above  which  15  feet  of  massive 
gray  sandstone  is  exposed.  A graphic  representation  of  this  bed  is 
given  in  PI.  XII,  Xo.  28;  No.  29  represents  an  exposure  of  the  same 
bed  in  a railroad  cut  one-half  mile  farther  west. 

SAGE  CREEK  AREA. 

LOCATION  AND  EXTENT. 

The  Sage  Creek  area,  situated  in  the  eastern  part  of  the  Great 
Falls  coal  field,  a few  miles  south  of  Stanford,  in  the  vicinity  of  Skull 
Butte,  lies  mainly  in  Tps.  15  and  16  N.,  Rs.  11  and  12  E.,  but  embraces 
small  portions  of  Tps.  15  and  16  N.,  R.  13  E.  The  area  described 
encircles  Skull  Butte,  where  the  dome-shaped  uplift  exposes  rocks 
older  than  the  coal-bearing  measures.  This  area  ranks  second  in  the 
field  in  point  of  size,  being  slightly  larger  than  the  Otter  Creek  area 
and  considerably  smaller  than  Sand  Coulee  area.  The  southern 


72 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


limit  of  the  Sage  Creek  coal  area  is  definitely  marked  in  most  places 
by  the  outcrop  of  the  coal,  but  to  the  north  and  to  a certain  extent 
to  the  east  and  west,  the  limits  of  the  workable  coal  must  be  inferred 
from  geologic  evidence.  In  Barnes  Coulee,  a tributary  of  Spring 
Draw,  which  is  the  easternmost  locality  at  which  the  coal  is  exposed 
within  the  area  investigated,  the  coal  bed  thins  from  more  than  7 
feet  on  the  west  side  of  the  coulee  to  less  than  3 feet  on  the  east  side, 
in  a distance  of  less  than  half  a mile.  The  relative  percentages  of 
shale  and  coal  change  rapidly  in  this  distance,  the  former  predom- 
inating on  the  east  side  of  the  coulee.  This  rapid  change  toward 
the  east  in  both  the  thickness  and  the  quality  of  the  coal  in  Barnes 
Coulee,  together  with  the  apparent  absence  of  workable  coals  for 
several  miles  farther  east,  is  regarded  as  sufficient  evidence  for  placing 
the  eastern  limit  of  the  Sage  Creek  coal  area  not  far  beyond  this  coulee. 

To  the  northeast,  farther  down  Sage  Creek  valley,  where  the  coals 
are  covered  by  an  increasing  thickness  of  overlying  rocks,  a number 
of  diamond-drill  prospect  holes  have  been  bored  in  order  to  ascertain 
the  thickness  of  the  coal  in  this  direction.  The  results  of  these  drill- 
ings have  not  been  made  public,  but  in  some  localities  the  drilling 
has  been  followed  by  shafting,  which  indicates  that  a bed  of  workable 
thickness  was  found.  The  northern  border  of  this  area  is  arbitrarily 
placed  a short  distance  beyond  the  Billings  and  Northern  Railroad 
from  the  eastern  limit  of  the  district  to  Stanford,  thence  westward 
nearly  to  Surprise  Creek,  and  thence  southwest  ward  to  the  coal 
outcrop  in  the  vicinity  of  Hazlett  Creek. 

On  Hazlett  Creek,  near  the  western  edge  of  the  area,  the  coal  has 
been  prospected  at  a number  of  places.  Here  the  bed  is  barely  of 
workable  thickness  and  is  very  shaly.  About  3 or  4 miles  farther 
north,  on  small  tributaries  of  Surprise  Creek,  the  coal  bed  is  repre- 
sented by  only  a few  inches  of  impure  coal,  associated  with  coaly 
shale.  The  same  is  true  on  Dry  and  Shannon  creeks,  farther  west. 
From  the  above  considerations  it  seems  probable  that  the  western 
limit  of  the  area  underlain  by  workable  coals  in  the  Sage  Creek  basin 
lies  somewhere  between  Hazlett  and  Surprise  creeks.  The  extent 
of  the  Sage  Creek  area  and  the  location  of  the  mines  and  prospects 
are  shown  on  PI.  II;  sections  of  the  beds  are  shown  in  PI.  XII. 

CHARACTER  AND  THICKNESS  OF  COAL  BED. 

So  far  as  known  there  is  only  one  coal  bed  in  this  area.  Its  thick- 
ness, including  partings,  ranges  from  6 to  18  feet.  Within  this 
thickness  of  beds,  deposited  under  coal-forming  conditions,  the  aggre- 
gate of  the  coal  ranges  from  2\  to  7 feet.  The  coal  usually  occurs 
in  the  form  of  three  distinct  benches,  which  are  generally  recognized 
by  miners  in  the  district.  The  lowest  bench  is  about  2 feet  thick 
and  is  regarded  as  the  best.  Above  this  is  commonly  a 2 to  6 inch 


COAL. 


73 


parting,  overlain  by  a middle  bench  12  to  16  inches  thick.  Next  is 
generally  1 to  6 inches  of  bone,  followed  by  the  uppermost  bench  of 
coal,  which  ranges  from  1 to  2 feet  in  thickness.  The  coal  is  usually 
covered  by  1 or  2 feet  of  dark-colored  shale,  which  forms  the  roof  of 
the  mine.  Above  the  shale  there  are  in  many  places  impure  coaly 
layers  interbedded  with  brown  and  black  sandy  leaf-bearing  shale 
having  a thickness  of  several  feet.  The  next  member  in  ascending 
order  is  a gray  massive  sandstone  ranging  in  thickness  from  20  to  60 
feet.  In  the  outer  portion  of  the  area  the  base  of  this  sandstone 
locally  forms  the  roof  of  the  mine. 

DEVELOPMENT. 

GENERAL  STATEMENT. 

The  coals  of  the  Sage  Creek  area  have  not  been  extensively  worked. 
Coal  has  been  mined  in  this  vicinity  for  many  years,  but  owing  to 
the  lack  of  transportation  facilities  the  output  has  never  exceeded 
the  amount  necessary  to  supply  a small  local  demand.  At  the  present 
time  mining  is  carried  on  at  only  three  small  mines,  owned  by 
Messrs.  Schultz,  Seman,  and  Hughes.  The  annual  output  of  the 
Schultz  mine  is  about  1,000  tons;  that  of  the  Seman  is  somewhat 
smaller.  Neither  of  these  mines  is  well  improved.  The  Hughes  mine 
has  only  recently  been  opened. 

MINES  OPERATED. 

Schultz  mine. — The  Schultz  mine,  the  largest  of  the  three  mines 
now  operated  in  this  district,  is  located  in  the  SE.  I SE.  I sec.  20, 
T.  15  N.,  R.  12  E.,  on  the  west  side  of  Spring  Draw,  a small  tributary 
of  Sage  Creek.  It  was  opened  in  1894,  and,  according  to  the  best 
information  obtainable,  though  operations  have  been  continuous, 
the  output  of  the  mine  has  never  been  large.  The  present  annual 
production  amounts  to  1,000  tons,  which  is  consumed  by  ranchmen 
and  inhabitants  of  small  towns  within  a radius  of  10  to  15  miles. 
The  coal  zone  has  an  aggregate  thickness  of  slightly  over  12  feet, 
but  only  the  coal  of  the  lower  half  is  mined,  none  of  that  in  the  upper 
part  being  regarded  as  of  sufficient  thickness  to  be  worked.  The 
coal  of  the  lower  part  occurs  in  three  benches,  which  have  a total 
thickness  of  4 feet  4^  inches,  not  including  the  6-inch  layer  of  bone 
1 foot  below  the  top  and  the  1 foot  of  bony  coal  2 feet  above  the  base. 
The  lowest  bench  is  2 feet  thick  and  constitutes  the  most  important 
coal  of  the  mine.  It  is  black,  with  a dull  luster,  and  contains  more 
or  less  pvrite  in  nodular  form.  The  middle  bench  has  a thickness 
of  about  16^  inches  and  generally  has  a bright  luster.  It,  too,  con- 
tains some  pvrite  nodules.  The  uppermost  bench  is  about  12  inches 
thick  and  is  generally  more  or  less  free  from  sulphur  (38).  Immedi- 
ately overlying  this  bench  in  the  upper  part  of  the  zone  is  a layer  of 


74 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 


bone  2 feet  thick,  which  forms  the  roof  of  the  mine.  This  is  followed 
by  12  inches  of  dark  sandy  shale  containing  thin  beds  of  coal,  which 
in  turn  is  overlain  by  21  inches  of  coal  containing  a small  percentage 
of  bone.  Above  this  coal  there  is  an  8-inch  layer  of  light-colored 
sandstone,  followed  by  6 inches  of  dark  coaly  shale  which  immediately 
underlies  massive  gray  sandstone  several  feet  in  thickness. 

Seman  mine. — The  Seman  mine  is  located  in  the  SW.  \ SE.  \ sec. 
20,  T.  15  N.,  R.  12  E.,  a few  hundred  yards  west  of  the  Schultz  mine 
and  on  the  same  side  of  Spring  Draw.  It  is  considerably  smaller 
than  the  Schultz  mine  and  is  worked  only  during  the  winter  months, 
having  a very  small  output,  which  rarely  exceeds  150  tons  a season. 
Coal  has  been  taken  out  of  this  opening  for  the  last  decade,  but  little 
attention  has  been  given  to  the  proper  development  of  the  under- 
ground workings. 

The  coal  bed  mined  here  is  almost  identical  with  that  worked  at 
the  Schultz  mine,  except  in  the  uppermost  bench,  which  appears  to 
be  somewhat  thicker.  Three  benches  occur;  the  lowest  bench  has 
a thickness  of  2 feet  and  is  overlain  by  9 inches  of  bony  coal.  Above 
this  is  the  middle  bench,  which  has  a thickness  of  16  inches  and  is 
followed  by  a 7-inch  layer  of  bone.  Next  is  15  inches  of  bright, 
firm-looking  coal,  which  constitutes  the  uppermost  bench.  A com- 
plete section  is  shown  in  PI.  XII,  No.  36.  The  deposit  has  the 
characteristic  shale  roof  and  clay  floor  exhibited  in  the  Schultz  mine. 

In  physical  properties  the  coals  of  the  different  benches  closely 
resemble  those  of  the  Schultz  mine.  The  characteristic  sulphur 
balls  are  present,  especially  in  the  lowest  bench;  the  middle  bench 
has  the  usual  bright  luster,  and  in  practical  use  these  two  coals  seem 
to  give  equal  satisfaction.  The  main  entry  extends  about  400  feet 
from  the  face  in  a meandering  but  westerly  direction.  About  200 
feet  from  the  mouth  of  this  entry  a side  entry  extends  at  right  angles, 
approximately  30  feet  to  the  south. 

Hughes  mine. — In  1904  a small  mine  was  opened  on  the  Hughes 
ranch,  on  the  east  side  of  Willow  Creek,  in  the  NE.  I sec.  19,  T.  15  N., 
R.  12  E.  This  mine  is  about  2 miles  northwest  of  the  Schultz  and 
Seman  mines,  near  the  southern  limit  of  the  Sage  Creek  area.  The 
total  thickness  of  the  bed  worked  is  5 feet  8 inches,  including  a 9-inch 
layer  of  bony  coal  16  inches  above  the  base  and  excluding  a 3-inch 
bed  of  true  bone  2 feet  below  the  top  of  the  bed.  Coal  occurs  in 
three  benches,  as  is  common  in  other  parts  of  the  area.  The  lowest 
bench  is  slightly  thinner  than  usual,  being  only  about  16  inches  thick. 
This  is  due  to  a 2-inch  layer  of  clay  that  occurs  at  the  base  of  the 
bench  and  separates  it  from  a 3-inch  bed  of  coal  not  mined  at  this 
place.  The  middle  bench  is  16  inches  thick  and  is  bright  and  firm, 
but  contains  a few  thin  layers  of  bone.  A 3-foot  bed  of  good-looking 
coal  constitutes  the  uppermost  bench.  It  is  overlain  by  dark-colored 


COAL. 


75 


sandy  shale,  which  forms  the  roof.  A graphic  section  of  the  bed  is 
given  in  PL  XII,  No.  34. 

ABANDONED  MINES. 

In  addition  to  the  above-described  mines,  there  are  in  the  Sage 
Creek  area  four  abandoned  mines  from  which  considerable  coal  has 
been  taken  during  the  last  ten  years.  These  are  the  Corwin  & 
McGregor  (now  owned  by  Mr.  Schultz),  the  Fisher,  the  West  Fork  of 
Willow  Creek,  and  the  Sage  Creek  Sheep  Company*  mines.  Graphic 
sections  of  all  except  the  Corwin  & McGregor  mine  are  given  in  PL 
XII,  Nos.  42,  43,  and  45. 

Corwin  <P  McGregor  mine. — The  abandoned  Corwin  & McGregor 
mine,  located  on  the  west  side  of  Spring  Draw,  between  the  Seman 
and  Schultz  mines,  was  one  of  the  first  to  be  operated  in  the  imme- 
diate vicinity,  and  it  has  probably  been  more  extensively  worked 
than  either  of  the  adjoining  mines.  At  the  face  of  this  opening  the 
coal  horizon  presents  the  usual  succession  of  beds,  but  they  were  too 
badly  weathered  to  permit  accurate  measurements  of  the  individual 
layers,  and,  as  the  mine  was  flooded,  the  underground  workings, 
could  not  be  examined. 

The  face  of  the  mine  presents  one  unusual  feature.  The  coal  in 
the  upper  part  of  the  coal  bed,  as  exposed  at  the  Schultz  mine,  here 
appears  to  have  reached  a thickness  of  2\  feet.  The  percentage  of 
this  bed  that  might  prove  to  be  coal  when  examined  on  a freshly 
exposed  surface  could  not  be  ascertained. 

Fisher  mine. — Another  abandoned  mine,  known  as  the  Fisher  mine, 
is  located  on  the  east  side  of  a low  hill  of  isolated  coal-bearing  rocks, 
which  occur  as  an  outlier  on  the  south  side  of  the  area,  in  the  SE.  J- 
sec.  13,  T.  15  N.,  R.  11  E.  It  has  not  been  worked  for  a number  of 
years,  but  to  judge  from  the  size  of  the  excavation,  considerable 
coal  has  been  taken  out  in  the  past.  The  bed  is  not  deeply  covered 
nor  extensive,  comprising  at  most  only  a few  acres,  and  for  this 
reason  probably  the  mine  was  abandoned.  It  is  very  doubtful  if 
the  deposits  are  sufficiently  extensive  to  warrant  any  further  develop- 
ment. A section  of  the  face  of  this  opening  is  given  in  PL  XII, 
No.  42. 

West  Fork  of  Willow  Creek  mine. — At  the  head  of  West  Fork  of 
Willow  Creek  there  is ‘an  abandoned  mine  from  which,  apparently, 
considerable  coal  has  been  taken  out,  but  it  has  caved  to  such  an 
extent  that  it  was  impossible  to  examine  the  details  of  the  under- 
ground workings.  It  is  located  near  the  southern  edge  of  the  coal 
area,  in  the  NW.  J sec.  13,  T.  15  N.,  R.  1 1 E.  A section  of  the  outcrop 
shows  very  poor  coal  in  the  lower  bench  (43). 

Sage  Creek  Sheep  Company  mine. — An  abandoned  opening  on  the 
north  side  of  Skull  Butte,  in  the  SW.  J sec.  31,  T.  16  N.,  R.  12  E.,  is 


76 


GEOLOGY  OF  GREAT  FALLS  COAL  FTELD,  MONTANA. 


known  as  the  Sage  Creek  Sheep  Company  mine.  A small  amount  of 
coal  was  taken  out  of  this  mine,  but  it  has  not  been  worked  for 
several  years  (45). 

PROSPECTS. 

Entry  prospects. — The  Sage  Creek  area  has  been  considerably  pros- 
pected for  coal.  In  many  of  the  coulees  where  the  coal  is  exposed 
small  openings  have  been  made  to  ascertain  the  character  and  thick- 
ness of  the  bed.  Some  of  these  prospects  have  caved  so  as  to  obscure 
the  coal  bed,  but  more  commonly  a good  section  can  be  obtained. 
In  Barnes  Coulee,  a small  tributary  of  Spring  Draw  on  the  east, 
the  coal  has  been  opened  at  five  or  six  places  on  either  side  of  the 
ravine.  J.  D.  Barnes  has  the  largest  prospect  in  this  vicinity.  It 
is  located  on  the  west  side  of  the  coulee  about  100  feet  up  the 
slope,  in  the  SE.  \ sec.  29,  T.  15  N.,  R.  12  E.  An  entry  has  been 
driven  80  feet  from  the  face,  which  exhibits  over  7 feet  of  coal  dis- 
tributed through  13  feet  of  coal-bearing  beds.  The  coal  is  overlain 
by  gray  sandstone  and  underlain  by  dark-colored  shale. 

Directly  opposite  the  Barnes  prospect  on  the  other  side  of  the 
coulee  the  coal  has  been  opened  at  five  places,  the  northernmost 
opening  being  an  entry  15  feet  deep  which  exhibits  4 feet  of  coal 
interbedded  with  considerable  bone.  About  150  feet  south  of  this 
prospect  another  opening  extends  120  feet  from  the  face,  showing 
3 feet  of  coal.  The  lower  21  inches,  however,  is  of  a very  inferior 
quality. 

About  400  feet  farther  south  on  the  same  side  of  the  coulee  the 
entry  of  another  small  abandoned  mine  extends  150  feet  from  the  face. 
At  the  mouth  the  coal  bed  has  a total  thickness  of  7 feet  2\  inches, 
with  only  18  inches  of  pure  coal  near  the  middle;  9 inches  below 
this  and  10  inches  above  the  bottom  of  the  section  there  is  an  11 -inch 
bed  of  bony  coal  (40).  At  the  end  of  the  main  entry,  150  feet  from 
the  mouth  of  the  mine,  the  section  shows  9|  inches  of  coal  at  the 
base,  which  probably  corresponds  to  the  11  inches  of  bony  coal  at 
the  mouth.  Overlying  the  9J-inch  layer  of  coal  is  12  inches  of  bone, 
corresponding  to  the  9 inches  of  true  bone  in  the  section  taken  at 
the  outcrop.  The  next  member  in  ascending  order  at  the  back  end 
of  the  entry  is  a 9-inch  bed  of  coal  followed  by  3 inches  of  shale,  and 
this  in  turn  by  12  inches  of  coal.  These  three  members  are  believed 
to  be  represented  in  the  outcrop  section  by  18  inches  of  coal.  The 
sections  at  the  outcrop  and  at  the  back  end  of  the  entry  are  shown 
in  PI.  XII,  Nos.  40  and  41. 

Nearly  300  yards  south  of  this  abandoned  mine  a small  prospect 
shows  very  bony  coal. 

A comparison  of  the  sections  in  these  five  prospects  on  the  east 
side  of  Barnes  Coulee  with  the  Barnes  prospect  on  the  opposite  side 


COAL. 


77 


indicates  not  only  that  the  percentage  of  coal  in  the  bed  is  decreasing 
to  the  east  but  that  the  quality  of  the  coal  is  rapidly  becoming  inferior 
in  that  direction. 

Diamond-drill  prospects. — Considerable  prospecting  has  been  done 
with  the  diamond  drill  in  the  Sage  Creek  coal  area,  mainly  to  deter-' 
mine  the  thickness  of  the  coal  bed  in  the  northern  part  of  the  field, 
where  the  gradual  dip  of  the  beds  to  the  northward  carries  it  consider- 
ably below  the  surface.  Five  borings  have  been  made,  as  follows: 

The  Sage  Creek  Sheep  Company’s  home-ranch  boring,  in  the  SW.  i 
sec.  14,  T.  15  X.,  R.  12  E.;  the  McComb  boring,  in  the  XE.  \ XE.  J sec. 
18,  T.  15  X.,  R.  12  E. ; the  upper  Sage  Creek  boring,  in  the  XE.  \ XW.  J 
sec.  2,  T.  14  X.,  R.  12  E.;  and  the  Dr}^  Coulee  boring,  in  the  SW.  \ 
SW.  i sec.  20,  T.  13  N.,  R.  12  E.  These  borings  are  said  to  range 
in  depth  from  300  to  900  feet,  but  no  definite  information  regarding 
the  thickness  of  the  coal  bed  or  the  depth  at  which  it  was  penetrated 
in  any  particular  well  could  be  obtained. 

CHARACTER  OF  COAL. 


GENERAL  STATEMENT. 

The  coal  of  the  Great  Falls  field  differs  in  physical  characteristics - 
as  well  as  in  chemical  composition  from  those  of  neighboring  fields 
in  Montana  and  northern  Wyoming.  As  it  occurs  in  rocks  of  Lower 
Cretaceous  age,  it  is  among  the  oldest  coals  in  this  general  region, 
the  nearest  contemporaneous  deposits  being  the  Cambria  coals  of  the 
Black  Hills  and  the  Lethbridge  coals  of  Canada.  It  is  of  the  same 
age  as  the  coal  of  Judith  basin  (which  in  reality  is  a part  of  the  same 
field)  and  is  considerabty  older  than  the  Bull  Mountain,  Miles  City, 
Sheridan,  and  Red  Lodge  coals,  most  of  which  are  of  Tertiary'  age. 
In  physical  properties  and  chemical  composition  it  shows  little 
regional  variation  and  closely  resembles  deposits  of  the  same  age  in 
Judith  basin  to  the  east.  It  also  bears  some  likeness  to  the  Cambria 
coals  of  the  Black  Hills. 

PHYSICAL  PROPERTIES. 

The  coal  of  the  Great  F alls  field  is  in  general  black  to  grayish  black 
in  color,  with  bands  of  pitch-black  coal  running  through  it.  A great 
part  of  the  coal  is  dull,  but  contains  thin  bands  of  bright  coal  which 
have  a vitreous  or  glassy  luster.  It  is  a moderately  dense  variety  of 
bituminous  coal  distinctly  bedded  and  characterized  by  a banded 
structure,  which  consists  of  alternating  layers  of  bright  and  dull 
coal  parallel  to  the  bedding.  The  bright  bands  range  in  thickness 
from  a mere  film  to  one-fourth  of  an  inch,  and  usually  constitute 
only  a small  percentage  of  the  whole,  the  duller  coal  greatly  predom- 
inating. A close  examination  of  the  dull  bands,  which  consist  partly 
of  mineral  charcoal  and  partly  of  dull-lustered  coal,  shows  that 


78  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

many  of  them  contain  minute  lenses  of  bright  coal,  giving  to  the  whole 
a schistose  appearance. 

The  coal  usually  separates  or  breaks  into  blocks  that  are  roughly 
rectangular  in  outline,  with  the  face  and  butt  cleat  nearly  at  right 
angles.  Even  where  fine  fragments  are  separated  either  by  crushing 
or  weathering  they  are  in  general  rudely  prismatic.  The  face  cleat 
commonly  presents  a smooth,  even  surface  having  a subdued  glisten- 
ing or  vitreous  luster;  the  butt  cleat  has  a more  irregular  surf  ace  and 
a much  brighter  luster.  The  fracture  of  the  dull  coal  is  irregular  or 
uneven,  but  that  of  the  bright  coal  is  small  conchoidal.  The  coal 
separates  more  or  less  easily  along  the  bedding  plane,  the  surface  of 
which  at  many  places  exhibits  blades  of  mineral  charcoal  lying  in 
different  directions,  the  whole  giving  a fibrous  texture  and  velvet 
luster.  Less  commonly  the  surface  of  the  bedding  plane  contains 
remnants  of  bright-lustered  coal  adhering  to  the  duller  variety.  It 
is  under  these  circumstances  that  the  bright  coal  exhibits  to  the  best 
advantage  its  small  conchoidal  fracture. 

The  dull  coal  is  moderately  soft  and  tough;  the  bright  coal  is  con- 
siderably harder  and  more  brittle.  The  hardness  of  the  former  is 
about  1 and  that  of  the  latter  about  2.5.  The  streak  ranges  from 
brown  to  brownish  black,  seldom  black.  The  coal  is  more  or  less 
sooty  and  soils  the  fingers  readily.  The  specific  gravity  varies  con- 
siderably in  different  benches  of  the  same  bed;  it  ranges  from  1.30  to 
1.70,  the  average  being  about  1.40. 

As  previously  stated,  sulphur  is  present  in  the  coal  in  considerable 
quantities.  It  occurs  in  the  form  of  iron-pyrite  nodules  which  are 
rudely  reniform  in  outline,  although  spherical  forms  are  not  uncom- 
mon. In  size  these  nodules  range  from  that  of  a pinhead  to  about 
4 inches  in  diameter,  the  average  being  about  1 inch.  Their  major 
axes  are  usually  parallel  with  the  bedding,  although  some  smaller 
nodules  are  seen  at  varying  angles  to  that  plane.  Few  of  them 
occur  in  joint  planes.  About  the  nodules  the  coal  shows  a foliated 
or  compressed  structure,  which  has  probably  been  developed  by  the 
force  exerted  in  the  crystallization  of  the  pyrite.  Resin  is  rarely 
present. 

The  minable  coal  is  separated  into  benches  by  carbonaceous  shale 
or  bone  and  by  bony  coal.  The  former  appears  to  be  of  fairly  uniform 
character  throughout  the  field.  It  has  shaly  structure  and  breaks 
with  subconchoidal  fracture.  It  is  grayish  black  in  color,  fine  grained 
and  homogeneous  in  character,  soft,  moderately  tough,  and  has  a 
specific  gravity  of  about  2.  It  is  usually  a true  parting  between  the 
coal  benches,  separating  easily  from  the  coal  both  above  and  below. 
In  thickness  it  ranges  from  a fraction  of  an  inch  to  1 foot,  the  average 
being  about  3 to  4 inches.  In  some  places  it  weathers  light  gray, 
standing  out  in  strong  contrast  to  the  coal. 


COAL. 


79 


CHEMICAL  PROPERTIES. 

During  the  investigation  here  reported  a number  of  samples  of  the 
coal  were  taken  in  different  localities  for  the  purpose  of  chemical 
analysis.  These  samples  were  collected  in  a uniform  manner.  A 
channel  was  cut  perpendicularly  across  the  face  of  the  coal  bed  from 
roof  to  floor,  of  such  a size  as  to  yield  at  least  5 pounds  of  coal  per  foot 
in  thickness  of  coal  bed.  All  material  encountered  in  tins  cut  was 
included  in  the  sample,  except  partings  more  than  tliree-eighths  of 
aminch  in  thickness,  and  lenses  and  concretions  of  sulphur  or  other 
impurities  greater  than  2 inches  in  diameter.  The  coal  thus  obtained 
was  pulverized  sufficiently  fine  to  pass  through  a sieve  of  half-inch 
mesh,  and  after  thoroughly  mixing  was  divided  into  quarters,  oppo- 
site quarters  being  rejected.  This  process  was  continued  until  the 
amount  was  reduced  to  about  a quart  sample.  The  material  was  then 
placed  in  a galvanized  can,  sealed  by  adhesive  tape,  and  shipped  to 
the  chemical  laboratory  of  the  Survey  fuel-testing  plant  at  St.  Louis, 
F.  M.  Stanton,  chemist  in  charge,  where  the  analyses  were  made. 


Analyses  of  coal  samples  from  Great  Falls  coal  field. 


Sage  Creek 
area. 

Otter  Creek  area. 

Sand  Coulee  area. 

Belt  district. 

Laboratory  No 

3750  | 

3753 

3758 

3759 

3757 

3515 

3512 

3514 

Analysis  of  sample  as  received: 

. ( 

Moisture 

11.26 

9.27 

10. 18 

8.76 

13.07 

3.51 

7.05 

6.37 

Volatile  matter 

25.85 

29.57 

24.82 

25.72 

21.79 

26.39 

25.47 

27.55 

o 

2 

Fixed  carbon 

46. 49 

45.90 

45.25 

50.36 

43.26 

50.60 

49.34 

45.20 

*1 

/Ash 

16.40 

15.26 

19.75 

15.16 

21.88 

19.50 

18.14 

20.88 

\ Sulphur 

4.56 

3.96 

3.01 

3.91 

1.30 

3.74  1 

1.67 

2.04 

Hydrogen 

4.51 

4. 78 

4.40 

4.23 

4.13  ; 

4.36 

3.92 

£ i 

Carbon 

53.47 

58.13 

58.93 

49.95 

! 61.51  ; 

58.10 

56. 14 

Nitrogen 

.69 

.79 

.79 

.69 

.60 

.64 

.73 

Oxvp-en 

20.37 

17.08 

16.81 

21.95 

10.44 

17.09 

16.29 

Calories. . . 

5, 122 

5, 675 

5,626 

4,639 

6, 045 

5,623 

5, 481 

British  thermal  units 

9,220 

10.215 

10.127 

8.350 

! 10.881  . 

10,121 

9,866 

Loss  of  moisture  on  air  drying 

5.50 

4.60 

4.60 

4.80 

6.00 

1.60 

1 2.60 

2.70 

Analysis  of  air-dried  sample: 

■ 1 

'Moisture 

; 6.09 

5.00 

5.85 

4.16 

7.52 

1.93 

4.57 

3.77 

gj 

Volatile  matter 

27.35 

31.00 

26.01 

27.02 

23.18 

26.81 

26.15 

28.30 

2 

Fixed  carbon 

49.18  | 

48.00 

47. 43 

52.90  i 

46.02 

i 51.44 

50.65 

46.46 

/Ash 

17.38 

16.00 

20.71 

15.92 

23.28 

; 19.82 

18.63 

21.47 

f\  Sulphur 

4.82 

4.15 

3.15 

4.11 

1.38 

3.80 

1.71 

2.08 

Hydrogen 

4.12 

4.48 

4.03 

3.79 

4.02 

4.17 

3.73 

— J 

Carbon 

56. 57 

60.93 

61.90 

53.14 

62.51 

! 59. 65 

57. 70 

5 

Nitrogen 

.73 

.83 

.83 

.73 

. 65 

.74 

Oxvffen 

16.38 

13.61 

13.21 

17.68 

| 9!  16 

i 15.19 

~ 14.28 

Calories 

5,420 

5, 949 

5,910 

4,951 

i 6.094 

5, 824 

5,633 

British  thermal  units 

9,756 

10, 707 

10,637 

8,888 

11,058 

10,391 

10, 139 

Fuel  ratio 

1.79 

1.55 

1.82 

1.96 

1.98 

1.91 

1.93 

1.64 

80 


GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTAXA. 


Analyses  of  coal  samples  from  Great  Falls  coal  field — Continued. 


Sand  Coulee  area. 

Belt  district.  CoSSdYstSt.  Smith  River  district. 


Laboratory  No 

3755 

3513 

3754 

4115 

4119 

4118  4117 

4114 

Analysis  of  sample  as  received  : 

. [ Moisture 

9.58 

4.62 

10.88 

6.01 

7.49 

4.82  6.17 

4.54 

- 1 Volatile  matter 

23.24 

30.51 

20.27 

28.43 

27.29 

27.17  27.03 

27.44 

*-■  | Fixed  carbon 

52.24 

46.14 

41.97 

51.42 

51.44 

46.13  52.03 

47.95 

rM  If  Ash 

14.94 

18.73 

26.88 

1 14.14 

13.78 

21.88  14.77 

20-07 

(1  Sulphur 

2.00 

3.59 

1.79 

2.38 

2.32 

2.84  4.36 

4.09 

^ Hydrogen 

— < Carbon 

4.28 
58.  74 

3.72 

47.37 

4.46 

63.61 

4.68 

62.21 

4.36  4.43 

56.98  61.62 

4.23 
58. 66 

p Nitrogen 

1 Oxygen. 

Calories. 

.67 

19.37 

5.518 

.52 
19.72 
4.301 
7.  742 

.91 
14.50 
6, 196 

.88 

16.13 

6,115 

11,007 

.72  .93 

13.22  13.89 

5,578  6,077 

10,040  10,939 

.87 

12.08 

5,818 

10,472 

British  thermal  units 

11.153 

Loss  of  moisture  on  air  drying ] 

5.00 

2.10  ; 

5.40 

2.40 

2.60 

1.90  2.20 

1.70 

Analysis  of  air-dried  sample: 

• [Moisture 

4.82 

2.57 

5.76 

3.70 

5.02 

2.98  4.06  1 

2.89 

g 1 Volatile  matter 

24.40 

31.17 

21.42 

29.13 

28.02 

27.69  27.63  ; 

27.91 

• '-1 1 Fixed  carbon 

55.00 

47.13  1 

44.42 

52.68 

52.81  1 

47.03  53.20  ; 

48.79 

^ NAsh 

15.72 

19.13  I 

28.40 

14. 49 

14.15 

22.30  15.11 

20.41 

[1  Sulphur 

2.10 

3.70 

1.89 

2.43 

2.38 

2.90  4.46 

4.13 

• Hydrogen 

3.91 

3.30 

4.33 

4.51 

4. 24  4. 25 

4. 18 

~ < Carbon 

61.85 

50.08 

65.17 

63.88 

58.08  63.02 

59.66 

Nitrogen 

1 Oxygen 

Calories 

.70 

15.72 

5,808 

.55 
15.78 
4,546 
8, 184 
2.07 

.92 

12.66 

6,348 

11,427 

1.81 

.89 
14. 19 
6,278 
11,300 

.73  .95 

11.75  12.21 

5,678  ! 6,213 
10,244  11,185 

1.70  1.93 

.88 

10.74 

5,918 

10,654 

1.75 

British  thermal  units 

10, 454 

Fuel  ratio 

2.25 

I 

1.51 

1.88 

The  analysis  of  each  coal  sample  is  given  in  two  forms,  one  showing 
the  composition  of  the  sample  as  received  at  the  laboratory,  which 
may  be  regarded  as  representing  the  condition  of  the  coal  in  the  mine, 
the  other  showing  the  composition  of  an  air-dried  sample.  Ultimate 
analyses  were  obtained  of  all  except  two  samples.  The  analyses 
under  laboratory  Nos.  3756,  3757,  and  3754  can  not  be  regarded  as 
representative  of  the  coals  of  this  field,  for  each  of  these  samples  was 
collected  in  a shallow  entry  near  the  surface,  and  consequently  con- 
tained weathered  coal.  Sample  No.  3754  was  obtained  on  the  margin 
of  a coal-bearing  area,  where  the  coal  was  recognized  in  the  field  to  be 
of  a quality  too  inferior  to  work. 

The  coal  of  the  Great  Falls  field  contains  on  an  average  about  49  per 
cent  of  fixed  carbon,  26  per  cent  of  volatile  matter,  18  per  cent  of  ash, 
and  3 per  cent  of  sulphur.  Its  fuel  ratio,  obtained  by  dividing  the 
percentage  of  fixed  carbon  by  the  percentage  of  volatile  matter, 
ranges  from  1 .51  to  2.07,  with  an  average  of  1.84.  The  calorific  value 
of  the  coal  is  good,  ranging  in  representative  samples  from  about 
10,000  to  11,500  British  thermal  units,  the  average  being  10,750  in  an 
air-dried  sample.  They  are  superior  in  this  respect  to  the  coals  of  Red 
Lodge,  the  next  largest  coal-producing  locality  in  Montana.  Their 
heat  value  is  also  considerably  higher  than  that  of  the  coals  of  the  Bull 
Mountain  and  eastern  Montana  fields.  The  coal  does  not  slack  to  any 
appreciable  extent  on  exposure  to  the  air.  Certain  benches  of  the 
coal  possess  coking  properties  and  formerly  a number  of  coke  ovens 


COAL. 


81 


were  operated  by  the  Anaconda  Copper  Mining  Company  at  Belt. 
The  separation  of  coking  from  noncoking  coal,  however,  was  too 
expensive  to  render  the  work  profitable,  and  the  ovens  were  aban- 
doned. As  a domestic  and  steam  fuel  it  gives  perfect  satisfaction  and 
its  relative  freedom  from  slacking  makes  it  a good  shipping  coal. 

From  the  analyses  and  the  physical  properties,  therefore,  the  coal  of 
the  Great  Falls  field  is  regarded  as  medium-grade  bituminous.  It  is 
superior  in  quality  to  the  Red  Lodge,  Bridger,  and  Sheridan  coals  of 
southern  Montana  and  northern  Wyoming,  and  compares  favorably  in 
composition  with  the  Cambria  coal  of  the  Black  Hills  region. 

FUTURE  DEVELOPMENT. 

The  Great  Falls  coal  field,  owing  to  its  geographic  position  with 
respect  to  other  coal  fields  and  the  quality  of  the  product  itself,  is  des- 
tined to  become  the  most  important  coal-mining  district  of  north-cen- 
tral Montana.  The  territory  which  this  field  may  be  expected  to  sup- 
ply with  coal  in  the  future  lies  mainly  to  the  north  and  northwest. 
To  the  southeast  there  are  a number  of  coal  localities  along  Mussel- 
shell River,  which  with  the  development  of  proper  railroad  facilities 
would  probably  become  large  coal-producing  districts.  Throughout 
the  area  bordering  the  Great  F alls  coal  field  on  the  north  different  con- 
ditions prevail.  Here,  although  coal-bearing  rocks  occupy  extensive 
areas  both  to  the  northeast  in  the  vicinity  of  Havre  and  to  the  north- 
west along  the  base  of  the  Rocky  Mountain  front  range,  yet  from  the 
best  information  which  can  be  obtained  the  area  underlain  by  coal  of 
workable  thickness' is  not  large  nor  are  the  deposits  of  high  grade,  so 
that  much  of  this  part  of  Montana  will  probably  be  supplied  from  the 
Great  F alls  field.  The  Lethbridge  coal  field,  north  of  the  international 
boundary  line,  is  a large  coal-producing  district,  but  with  the  present 
tariff  of  60  cents  per  ton  and  the  increasing  settlement  of  this  part  of  the 
British  possessions  much  of  the  output  will  probably  be  consumed  in 
Canada,  leaving  a relatively  small  amount  to  be  shipped  into  Montana. 

A summary  of  the  transportation  facilities,  present  and  prospective, 
has  already  been  given  (p.  20).  Another  factor  to  be  considered  in 
the  general  development  of  this  region  is  the  unharnessed  water  power 
contained  in  the  Great  Falls  of  Missouri  River,  located  a few  miles 
below  the  town  of  Great  Falls.  At  present  the  Black  Eagle  Falls,  one 
of  the  smallest  and  the  only  one  of  this  series  of  cataracts  which  has 
been  utilized,  furnishes  power  for  the  large  smelters  owned  by  the 
Boston  and  Montana  Consolidated  Copper  Mining  Company,  the 
Royal  Milling  Company’s  flour  mills,  and  other  minor  industries. 
With  the  proper  utilization  of  Rainbow,  Crooked,  and  Big  Falls, 
located  farther  down  the  river,  sufficient  power  could  be  generated  to 
supply  many  more  large  industrial  enterprises.  The  presence  of  so 
54937— Bull.  356—09 6 


82  GEOLOGY  OF  GREAT  FALLS  COAL  FIELD,  MONTANA. 

large  an  amount  of  undeveloped  water  power  within  a relatively  short 
distance  of  the  large  mining  centers,  Butte  and  Anaconda,  makes 
Great  Falls  a favorable  site  for  smelters. 

The  Great  Falls  region  was  formerly  a grazing  district  and  only 
sparsely  populated.  Small  tracts  of  land  were  irrigated  here  and 
there  along  the  valleys,  but  with  the  growth  in  population  and  the 
increased  demand  for  agricultural  produce  irrigation  began  to  be 
more  generally  practiced  along  the  larger  streams,  resulting  eventu- 
ally in  the  construction  of  several  large  canals  by  private  individuals 
or  small  companies  organized  among  the  ranchmen.  Extensive  oper- 
ations are  now  being  carried  on,  both  by  the  Government  and  by  pri- 
vate enterprise,  to  reclaim  larger  tracts  of  land  along  Sun  and  Teton 
rivers  and  the  highland  lying  between  these  two  streams. 

Although  the  Great  Falls  district  is  not  at  present  very  thickly  set- 
tled, it  is  believed  that  the  increasing  railroad  facilities,  the  comple- 
tion of  the  Government  irrigation  projects,  which  will  reclaim  thou- 
sands of  acres  of  fertile  farming  land,  and  the  almost  unparalleled 
advantages  for  the  development  of  water  power  will  combine  to  cause 
a rapid  increase  in  population  within  the  next  decade.  This  increase 
will  be  attended  by  an  increased  demand  for  coal,  both  for  domestic 
and  steam  purposes,  and  though  the  coal  is  only  of  medium  grade  and 
the  deposits  are  not  extensive,  it  is  believed  that  the  Great  Falls  coal 
field  will  experience  material  development  within  the  next  few  years. 

TIMBER. 

The  area  included  in  this  report  is  essentially  a grazing  district,  with 
very  little  timber  except  along  the  valleys  of  the  larger  streams,  where 
deciduous  trees  are  more  or  less  abundant,  and  along  the  hilly  zones 
bordering  the  mountains,  where  there  is  a scanty  growth  of  coniferous 
forests.  The  Little  Belt  Mountains  to  the  south  are  irregularly  for- 
ested throughout  a considerable  part  of  the  uplift,  and  though  there 
have  been  numerous  fires,  large  areas  of  good  timber  remain.  Nearly 
all  the  districts  containing  valuable  timber  lie  inside  the  Little  Belt 
Mountain  Forest  Reserve,  the  location  of  which  is  shown  on  the  index 
map  (PI.  I).  The  most  abundant  trees  growing  in  the  Little  Belt 
Mountains  are  lodgepole  pine,  red  fir,  and  Englemann  spruce.  Of 
these  species  the  red  fir  is  most  extensively  used  for  mine  timbering  in 
the  Great  Falls  coal  field,  much  of  the  supply  being  derived  by  rail 
from  the  Neihart  district  of  the  Little  Belt  Range.  For  some  of  the 
smaller  mines,  however,  timber  is  procured  in  the  foothills  belt  and 
hauled  overland.  The  fact  that  all  the  larger  mines  are  located  out  on 
the  plains,  at  some  distance  from  the  forested  area  of  the  mountains, 
makes  timber  an  expensive  item  in  mine  operations,  especially  at 
Stockett  and  Sand  Coulee,  which  are  farthest  from  the  source  of 
supply. 


INDEX. 


A.  Page. 

Alluvium,  character  and  distribution  of 22, 43 

Altitudes,  range  of 14-16 

American  Smelting  and  Refining  Company 

mine,  description  of 59-60 

Anaconda  Copper  Mining  Company  mine, 

description  of 54-56 

view  at 56 

Armington,  coal  at 52 

description  of 21 

Arrow  Creek,  drainage  of 14, 19 

B. 

Barnes  Coulee,  coal  in 76 

Belt,  coal  at 52,53 

description  of 20 

Belt  Butte,  section  at 37 

Belt  Creek,  coal  of 18, 51, 54-60 

coal  of,  analyses  of. 79-80 

sections  of 54 

drainage  of 14, 15, 18-19 

mines  on 54-60 

sections  on '26 

plates  showing 20,30 

view  of 18 

Bibliography  of  region 7-14 

Bickett  mine,  description  of 67 

Black  Eagle  Falls,  development  at 16,81 

Boston  and  Montana  mine,  description  of 58-59 

Boston  Coulee,  coal  on 18 

drainage  of 16, 17, 18 

structure  in 49 

Boxelder  Creek,  coal  on 19 

drainage  of 15, 19 

Brady  mine,  description  of 59 

Brown  mine,  description  of 65 

Building  stone,  occurrence  of 50 

Buzzo  mine,  description  of 58 

C. 

Calhoun,  F.  H.  H.,  on  glacial  geology  of  re- 
gion  9,40-42 

Calvert,  W.  R.,  work  of 7,27 

Carboniferous  rocks,  character  and  distri- 
bution of 23-27 

Carville  mine,  description  of 66-67 

Cascade,  description  of 21 

“ Cascade  ” formation,  character  and  distribu- 
tion of 30-31 

“Castle”  limestone,  character  and  distribu- 
tion of 24-25 

fossils  of 24 

Cement  materials,  occurrence  of 50 

Chamber  Brothers’  mine,  description  of 70 

Clingan,  E.  R.,  prospect  of 60 


Page. 


Coal,  analyses  of 79-81 

character  of 77-81 

occurrence  of 15,50-51 

detailed  descriptions  of 51-77 

production  of 54 

Coal  beds,  character  and  thickness 52-53 

development  of 53-54 

structure  of 47-48 

Coal  lands,  location  of,  map  showing 7 

Colorado  shale,  character  and  distribution  of. . 22, 

36-38 

fossils  of 38 

section  of 37 

Corwin  & McGregor  mine,  description  of 75 

Cottonwood  Coal  Company  mine,  description 

of 61-63 

view  of 62 

Cretaceous  rocks,  character  and  distribution 

of 22,30-38 

Culture,  description  of 20-21 

D. 

Dahn  mine,  description  of 65 

Davis,  W.  M.,  on  Littlebelt  Mountains 8 

Development  of  region,  future 81-82 

Diamond-drill  borings,  location  of 60, 77 

Dikes,  character  and  distribution  of 45-47 

Domes,  description  of 48-49 

Drainage,  description  of 16-19 

Drift,  character  and  distribution  of 41 

Dune  sand,  character  and  distribution  of 43-44 

E. 

Eakin,  H.  M.,  work  of 7 

Economic  geology,  description  of 50-82 

Eldridge,  G.  H.,  on  Great  Falls  coal  field 8 

Ellis  formation,  character  and  distribution  of.  23, 

27-28 

fossils  of 28 

section  of 28 

F. 

Faults,  character  and  distribution  of 49 

Fire  clay,  occurrence  of 50 

Fisher  mine,  description  of 71,75 

Flood,  fossils  near 34 

Fontaine,  W.  M.,  on  flora  of  region 8 

G. 

Geologic  map  of  region Pocket 

Geology,  account  of 21-50 

Geology,  economic,  description  of 50-82 

Gerber  mine,  description  of 64 

Geyser,  fossils  from 38 

Geyser  Creek  basin,  fossils  of 34 


83 


84 


INDEX. 


Page.  ( 

Gibson  mine,  description  of 67 

Giffen  Coulee,  coal  in 19,52 

drainage  of 19 

Gilmore,  C.  W.,  fossils  determined  by 31,38 

Girty,  G.  H.,  fossils  determined  by 25,27 

Glacial  deposits,  character  and  distribution 

of 22,41-43 

Goodwin  Coulee,  drainage  of 16, 17, 18 

Gravels,  character  and  distribution  of 22,39-41 

Great  Falls  (town),  description  of 20 

Great  Falls  of  Missouri  River,  descriptions  of.  8, 16 

power  at 81-82 

Gypsum,  occurrence  of 50 

II. 

Hazlett  Creek,  coal  on 72 

fossils  on 33-34 

Hazlewood,  A.  J.,  work  of 7 

Herman  & Powell  mine,  description  of 59 

Highwood  Mountains,  location  of 14 

structure  in 50 

Hill  mine,  description  of 58 

Hoag’s  prospect,  location  of 68 

Hound  Creek,  coal  on 17 

drainage  of 17 

Hughes  mine,  description  of 74-75 

Igneous  rocks,  bibliography  of 45 

character  and  distribution  of 44-46 

J. 

Johannsen,  Albert,  on  rock  from  Belt  Butte.  37 

on  rock  from  Big  Belt  Mountains 46 

Jurassic  rocks,  character  and  distribution 

of 23,27-30 

K. 

Kibbey  sandstone,  character  and  distribution 

of 25 

Knowlton,  F.  H.,  fossils  determined  by 33-34 

Kootenai  formation,  bibliography  of 35-36 

character  and  distribution  of 22,30-36 

coal  of 15, 50-51 

fossils  of 33-35 

section  of 32-33 

L. 

Laccoliths,  intrusion  of 48,50 

Lake  deposits,  character  and  distribution 

of 22,42-43 

sections  of,  figures- showing 42,43 

Larson  mine,  description  of 71 

Lewis,  M.,  on  Great  Falls 8 

Literature  on  region 7-14 

Little  Belt  Mountains,  location  of 14 

structure  of 49-50 

Location  of  area 7 

map  showing Pocket. 

Love  mine,  description  of 67-68 

M. 

McKinsey  mine,  location  of 66 

Madison  limestone,  character  and  distribu- 
tion of 23-25 

fossils  of 24 

views  of 24, 28 


Page. 

Map,  showing  coal  lands 7 

Map,  geologic,  of  region 7 

Metamorphic  codes,  character  and  distribu- 
tion of 46-47 

Millard  mine,  description  of 57 

Ming  Coulee,  coal  in 17-18, 52 

drainage  of 16-17 

fossils  of 24 

section  on,  plate  showing 30 

structure  in 48 

Missouri  River,  drainage  of 16-17 

fossils  from 35 

Mitchell  mine,  location  of 66 

Morainal  deposits,  character  and  distribution 

of 22,41-43 

Morrison  shale,  character  and  distribution 

of 23,28-30 

fossils  of 30 

section  of 29-30 

Mortson,  O.  C.,  work  of 7 

Mount  Oregon  Coal  Company  mine,  descrip- 
tion of 64-65 

Mowry  shale  member,  occurrence  of 36 

Muddy  Creek,  drainage  of 16 

N. 

Neel  Creek,  coal  on 18-19, 60 

drainage  of 18 

Nelson  mines,  description  of 63-64 

v5ew  of 62 

Newberry,  J.  S.,  on  fossils  of  region 8,33 

Niobrara  formation,  occurrence  of 36 

Nollar  mine,  description  of 70 

Nullinger  mine,  description  of 70-71 

O. 

Orr  mine,  description  of 57-58 

Otter  Creek,  coal  on 19,52 

drainage  of 14, 15, 18 

Otter  Creek  area,  coal  of 69 

coal  of,  analyses  of 79 

sections  of 70 

development  in 69 

location  and  extent  of 68-69 

mines  of 70-71 

Otter  Creek  divide,  location  of 14 

Otter  shale,  character  and  distribution  of 25 

P. 

Patterson  mine,  description  of 67 

Pirsson,  L.  V.,  on  geology  of  region 8-9 

Plains  province,  structure  of 47-49 

Pollock,  J.  P.,  work  of 7 

Population,  data  on 20-21 

Q- 

Quadrant  formation,  character  and  distribu- 
tion of 23, 25-27 

fossils  of 27 

section  of 25-26 

view  of 24 

Quaternary  deposits,  character  and  distribu- 
tion of 22, 39-44 

R. 

Railroads,  access  by 20 

Reclamation,  progress  of 82 

Relief,  description  of 14-16 


INDEX. 


85 


Page. 

Rice  mine,  description  of 67 

Riceville,  rocks  near 25 

rocks  near,  section  oi 25-26 

view  near 24 

Richardson  mine,  description  of 57 

Robbins,  S.  B.,  work  of 7 

Rock,  formations,  description  of 21-47 

distribution  of 22-23 

Running  Wolf  Creek,  drainage  of 19 

S. 

Sage  Creek,  coal  on 19 

drainage  of 19 

Sage  Creek  area,  coal  of 72-73 

coal  of,  analyses  of 79 

section  of 70 

development  of 73-77 

location  and  extent  of 71-72 

mines  of 73 

Sage  Creek  Sheep  Company  mine,  description 

of 75-76 

Salisbury,  R.  D.,  on  glacial  drift 42 

Sands,  dune,  character  and  distribution  of. . 43-44 

Sand  Coulee  (town),  coal  at 52, 53 

description  of 20-21 

Sand  Coulee,  coal  of 19 

coal  of,  sections  of 60 

drainage  of 15, 19 

mines  on 60-66 

structure  in 48 

plate  showing 28 

Sand  Coulee  area,  coal  of 52-68 

coal  of,  analyses  of - - 79-80 

development  in 53-54 

location  and  extent  of 51-52 

Sarzin  mine,  location  of 66 

Schmauch  mine,  description  of 57 

Schultz  mine,  description  of 73-74 

Sedimentary  rocks,  description  of 24-44 

Seman  mine,  description  of 74 

Skull  Butte,  description  of 15 

fossils  of 34 

section  at 32-33 

structure  of 48 

Skull  Creek,  coal  on 19 

drainage  of 19 

Smelters,  location  of 20 

Smith  River,  coal  of 53 


Page. 

Smith  River,  coal  of,  analyses  of 80 

sections  of,  plate  showing 54 

drainage  of 15, 17-18 

section  on 29 

Smith  River,  mines  on 66-68 

Spanish  Coulee,  fossils  of 34 

Stainsby  mine 65-66 

Stanford  Butte,  description  of 15 

gravels  on 39-40 

Stanford  conglomerate,  occurrence  of 39 

Stanton,  T.  W.,  fossils  determined  by 20,38 

Stockett,  coal  near CO-66 

coal  near,  analyses  of 80 

description  of 20 

fossils  from 24 

view  at 28 

structure  at 48 

Straight  Coulee,  coal  on 19,52 

drainage  of 19 

Stratigraphy,  description  of 21-47 

outline  of 21-23 

section  showing 30 

Structure,  description  of 47-50 

Sim  River,  drainage  of 17 

Surprise  Creek,  drainage  of 19 

T. 

Terraces,  occurrence  and  character  of 39-41 

Tertiary  deposits,  character  and  distribution 

of  22,39-44 

Timber,  condition  of 82 

Topography,  description  of 14-19 

U. 

Ulm  Bench,  description  of 16 

U pham,  W arren,  on  glacial  geology  of  region . . 9 

V. 

Volcanic  ash,  occurrence  of 37 

W. 

Watson  mine,  description  of 59 

Weed,  W.  H.,  on  geology  of  region. . 25,26,31-32,51 

on  Montana  coals 8-9 

Williams  Creek,  mines  on 71 

Willow  Creek,  coal  on 19 

drainage  of 19 

Willow  Creek  (West  Fork),  mine  on 75 

Winchester,  D.  E.,  work  of 7 


O 


I 


DEPARTMENT  OF  THE  INTERIOR 
UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  Director 


Bulletin  357 


PRELIMINARY  REPORT 

ON  THE 

COALINGA  OIL  DISTRICT 

FRESNO  AND  KINGS  COUNTIES 

CALIFORNIA 


BY 

RALPH  ARNOLD  and  ROBERT  ANDERSON 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1908 


CONTENTS. 


Page. 

Introduction «s 7 

General  features  of  the  district 7 

Plan  of  the  present  report 7 

Acknowledgments 9 

Advantage  of  cooperation  among  operators 10 

Geography  and  topography 11 

Location 11 

Definitions  of  place  names 12 

General  topographic  features ' 16 

Geology 19 

General  statement 19 

Stratigraphy 20 

Franciscan  formation 20 

Knoxville-Chico  rocks 21 

Tejon  formation 23 

The  post-Eocene  formations 29 

Yaqueros  sandstone 31 

Santa  Margarita  formation 35 

Jacalitos  formation 40 

Etchegoin  formation 46 

Paso  Robles  formation 56 

Terrace  deposits  and  alluvium 61 

Igneous  rocks 61 

Structure 62 

Cross  structures  and  their  topographic  influence 62 

Periods  of  movement  and  effect  on  formations  of  different  ages 63 

Main  lines  of  structure 64 

Character  of  the  folds  and  faults. : 67 

The  oil 68 

Occurrence 68 

Oil  zones 68 

Accumulation  of  the  oil 70 

Gravity  of  the  oil 71 

Relations  of  water  to  oil 72 

Origin  of  the  oil 73 

The  oil  fields : 74 

Subdivisions 74 

Contour  map 74 

Explanation 74 

Use  of  the  map 74 

Basis  of  the  contour  map 75 

Difficulties  of  preparation  and  degree  of  accuracy 75 


3 


4 


CONTENTS. 


The  oil  fields — Continued.  Page. 

Details  of  the  productive  areas 76 

Oil  City  field 76 

Location 76 

Geology  and  structure 76 

Geology  of  the  wells 77 

Product 78 

Eastside  field 79 

Peerless-Calif ornia  Diamond -T.  C.  area 79 

Location 79 

Geology  of  the  wells 79 

Product 81 

Technology 82 

Standard-Caribou-California  Monarch  area 82 

Location 82 

Geology  of  the  wells 82 

Product 83 

Standard-Calif  ornia  Oilfields  (sec.  27)  area 84 

Location 84 

Geology  of  the  wells 84 

Product 85 

California  Oilfields  (sec.  34)-Coalinga-Mohawk  area 86 

Location 86 

Geology  of  the  wells 86 

Product 87 

Standard-Stockholders-Hanford  area 87 

Location 87 

Geology  of  the  wells 88 

Product 88 

Westside  field 89 

Call-Confidence  area 89 

Location 89 

Geology  of  the  wells 89 

Product 91 

Mercantile  Crude-S.  W.  & B.  area 91 

Location 91 

Geology  of  the  wells 91 

Product 93 

Zier-Porter  and  Scribner-M.  K.  & T.  area 93 

Location 93 

Geology  of  the  wells 93 

Product 95 

Associated-Caledonian-Union  area 96 

Location 96 

Structure 96 

Geology  of  the  wells 96 

Product 98 

Area  between  Waltham  Creek  and  San  Joaquin  Valley  coal  mine. . 99 

Location 99 

Geology 99 

Structure 102 

Geology  of  the  wells 104 

Sec.  2,  T.  21  S.,  R.  14  E.,  and  vicinity 106 

Geology  of  the  wells 106 

Product 107 


ILLUSTRATIONS. 


0 


The  oil  fields — Continued. 

Details  of  the  productive  areas — Continued.  Page. 

Kreyenhagen  field 107 

Location 107 

General  geology  and  occurrence  of  oil 108 

Geology  of  the  wells 108 

Kettleman  Hills  field Ill 

Location Ill 

Geology  and  indications  of  oil 112 

Geology  of  the  wells 112 

Future  development 113 

General  statement 113 

Areas  discussed 114 

Northwest  of  Eastside  field 114 

Eastside  field 115 

Anticline  Ridge  and  Guijarral  Hills 116 

Westside  field 117 

Jacalitos  anticline 118 

Reef  Ridge  south  to  Dagany  Gap 119 

Kettleman  Hills 120 

Production 124 

Transportation  facilities 125 

Mineral  lands 126 

Oil  companies  and  oil  wells  in  the  district 127 

Survey  publications  on  petroleum  and  natural  gas 136 

Index 139 


ILLUSTRATIONS. 


Page. 

Plate  I.  Geologic  and  structural  map  of  the  Coalinga  district In  pocket. 

II.  Structural-contour  map  of  the  Coalinga  field In  pocket. 

Fig.  1.  Index  map  of  a part  of  southern  California 9 


PRELIMINARY  REPORT  ON  THE  GEOLOGY  AND  OIL 
RESOURCES  OF  THE  COALINGA  DISTRICT, 
FRESNO  AND  KINGS  COUNTIES,  CAL. 


By  Ralph  Arnold  and  Robert  Anderson. 


INTRODUCTION. 

General  features  of  the  district. — The  Coalinga  district  is  a strip  of 
land  about  50  miles  in  length  by  15  miles  in  width  lying  along  the 
northeastern  base  of  the  Diablo  Range  in  western  Fresno  and  Kings 
counties,  Cal.  The  region  is  accessible  by  rail  from  the  main  lines  of 
both  the  Southern  Pacific  and  the  Atchison,  Topeka  and  Santa  Fe 
railroads  by  a branch  line  running  westward  from  Goshen  to  the  town 
of  Coalinga.  The  proved  productive  territory  includes  a band  13 
miles  long  by  3 miles  wide,  lying  at  the  northern  end;  and  a narrow 
strip  along  the  southwestern  boundary.  The  oil  originated  in  the 
organic  Tejon  (Eocene)  shales  and  is  accumulated  in  interbedded 
sands  of  the  same  formation  and  also  in  sands  of  the  Vaqueros  (lower 
Miocene),  Santa  Margarita  (upper  middle  Miocene),  and  Jacalitos 
(upper  Miocene)  formations,  the  Vaqueros  being  the  principal  pro- 
ducer. The  wells  range  in  depth  from  600  to  over  3,300  feet,  and 
penetrate  from  20  to  more  than  200  feet  of  productive  sands.  The 
product  varies  from  a black  oil  of  14°  or  15°  Baume  to  a greenish  oil 
of  35°  Baume  or  better.  The  yields  range  from  3 or  4 barrels  a day 
for  individual  wells  in  the  Oil  City  field  to  as  much  as  3,000  barrels  a 
day  for  the  deeper  holes  in  the  Eastside  field.  The  total  production 
of  the  district  in  1906  was  7,991,039  barrels;  in  1907  it  was  8,871,723 
barrels,  and  in  1908  it  will  probably  exceed  12,000,000  barrels. 
According  to  the  figures  for  1907  the  district  ranks  third  in  production 
among  the  oil-producing  districts  of  the  State. 

Plan  of  the  present  report. — During  the  last  half  of  1901  and  the  first 
half  of  1902  George  H.  Eldridge,  of  the  United  States  Geological  Sur- 
vey, made  more  or  less  detailed  examinations  of  the  various  California 
oil  districts,  with  the  expectation  of  preparing  a monograph  on  the 

7 


8 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


oil  resources  of  the  State.  On  his  return  from  field  work  he  wrote  a 
brief  resume  of  the  results  obtained,  and  this  was  published  in  “Con- 
tributions to  Economic  Geology  for  1902. ”a  Later  he  began  the 
preparation  of  detailed  reports  on  each  field,  but  his  lamented  death 
in  June,  1905,  cut  short  this  work.  In  the  fall  of  1905  the  senior 
author  of  this  report  was  instructed  to  complete  the  work  begun  by 
Mr.  Eldridge,  and  by  the  middle  of  1907  detailed  reports  on  all  of  the 
oil  districts  in  the  counties  bordering  the  coast  had  been  made  ready 
for  the  press.6 

The  summer  and  fall  of  1907  were  spent  by  the  writers  in  making 
a detailed  geologic  investigation  of  the  Coalinga  field  proper  and  of  the 
territory  south  of  it  as  far  as  the  Kings  County-Kern  County  line  near 
Dudley.  In  order  to  make  the  results  of  this  investigation  available 
as  soon  as  possible,  it  has  been  deemed  expedient  to  prepare  the  fol- 
lowing preliminary  report.  This  will  be  followed  later  by  a bulletin 
containing  more  detailed  descriptions  of  the  conditions,  more  com- 
plete maps,  sections,  and  other  illustrations,  and  chemical  analyses 
and  calorific  tests  of  a large  number  of  the  oils.  The  location  of  the 
Coalinga  district  and  the  other  oil  fields  of  southern  California  are 
shown  in  fig.  1 . 

For  the  benefit  of  those  using  this  and  other  geologic  reports  on  the 
California  oil  fields,  it  must  be  stated  that  these  publications  are 
intended  to  be  as  thoroughly  scientific  discussions  as  possible,  and 
that  they  assume  on  the  part  of  the  reader  a general  knowledge  of 
the  fundamental  facts  and  conceptions  on  which  any  searching  study 
of  the  composition,  mineral  deposits,  and  history  of  the  earth  must  be 
based.  The  reports  may  be  criticised  as  being  too  technical  and  as 
not  easily  comprehensible  by  the  ordinary  reader,  but  the  treatment 
adopted  is  the  only  one  possible,  because  the  thorough  discussion  of 
the  subject  involves  a certain  amount  of  technical  knowledge  and 
the  use  of  exact  terms.  Explanatory  discussions  have  been  inserted 
wherever  it  seemed  possible  to  do  so  without  making  the  reports  too 
bulky  or  diminishing  their  scientific  value.  For  explanations  of  the 
principles  of  geology  or  the  meaning  of  terms  the  reader  is  referred  to 
any  one  of  the  numerous  text-books  of  geology.0 

a Eldridge,  G.  H.,  The  petroleum  fields  of  California:  Contributions  to  economic  geology,  1902:  Bull. 
U.  S.  Geol.  Survey  No.  213, 1903,  pp.  306-321.  (The  part  relating  particularly  to  the  Coalinga  district  is 
on  pages  306-308.) 

b Eldridge,  G.  H.,  and  Arnold,  Ralph,  The  Santa  Clara  Valley,  Puente  Hills,  and  Los  Angeles  oil  dis- 
tricts, southern  California:  Bull.  U.  S.  Geol.  Survey  No.  309,  1907. 

Arnold,  Ralph,  and  Anderson,  Robert,  Preliminary  report  on  the  Santa.  Maria  oil  district,  Santa 
Barbara  County,  Cal.:  Bull.  U.  S.  Geol.  Survey  No.  317,  1907. 

Arnold,  Ralph,  Geology  and  oil  resources  of  the  Summerland  district,  Santa  Barbara  County,  Cal.: 
Bull.  U.  S.  Geol.  Survey  No.  321, 1907. 

Arnold,  Ralph,  and  Anderson,  Robert,  Geology  and  oil  resources  of  the  Santa  Maria  oil  district, 
Santa  Barbara  County,  Cal.:  Bull.  U.  S.  Geol.  Survey  No.  322, 1908. 

c Any  of  the  following,  besides  various  others,  will  be  found  useful:  Dana,  Text-book  of  Geology; 
Le  Conte,  Elements  of  Geology;  Chamberlin  and  Salisbury,  Geology  (3  parts);  Geikie,  Text-book  of 
Geology. 


INTRODUCTION. 


9 


Acknowledgments. — The  writers  wish  to  acknowledge  their  indebt- 
edness to  the  late  George  H.  Eldridge  for  notes  collected  by  him  dur- 
ing his  examination  of  the  field.  Acknowledgment  is  also  due  to 
other  previous  workers  in  the  field,  among  whom  are  W.  L.  Watts, 
Frank  M.  Anderson,  John  H.  Means,  and  H.  R.  Johnson. 


Fig.  1. — Index  map  of  a part  of  southern  California,  showing  location  of  the  Coalinga  oil  field 
and  of  the  other  productive  oil  fields  of  the  State. 


The  value  and  accuracy  of  a report  like  the  present  one,  including 
as  it  does  a discussion  of  the  geology  of  developed  territory,  depends 
largely  upon  the  amount  and  accuracy  of  the  well  data  available  for 
use  in  its  preparation.  Certain  facts  may  be  gleaned  from  a critical 
examination  of  the  surface  outcrops  in  any  field,  and  many  helpful 
conclusions  may  be  deduced  from  a study  of  the  facts  thus  obtained. 
A comparison  of  the  conditions  met  with  in  a given  territory  with  those 


10 


COALING  A OIL  DISTRICT,  CALIFORNIA. 


in  other  better  known  fields  may  also  be  of  great  assistance,  but  for 
furnishing  specific  information  regarding  the  occurrence  of  the  oil  in 
any  particular  area  there  is  just  one  instrument,  and  that  is  the  drill. 

From  the  drilling  of  wells  in  the  Coalinga  field  during  the  last  ten 
years  a large  body  of  useful  data  concerning  the  underground  condi- 
tions has  been  accumulated,  and  whatever  accuracy  and  value  there 
is  in  the  underground  map  and  in  the  statements  concerning  the 
geology  of  the  wells  in  this  report  is  due  almost  entirely  to  the  gen- 
erosity of  the  operators  in  this  field  in  supplying  the  information. 
The  writers  therefore  wish  to  acknowledge  their  indebtedness  to  the 
officers,  managers,  and  other  operators  of  the  different  oil  companies 
for  their  hearty  cooperation  and  support.  Thanks  are  due  more  par- 
ticularly to  Messrs.  Jas.  H.  Pierce,  W.  W.  Orcutt,  S.  A.  Guiberson,  jr., 

R.  W.  Dallas,  A.  and  H.  Kreyenhagen,  A.  M.  Anderson,  H.  G.  Ander- 
son, J.  M.  Atwell,  Charles  Bab  tie,  Gordon  M.  Baker,  R.  C.  Baker, 
Balfour  Guthrie  & Co.,  Orlando  Barton,  H.  J.  Bender,  Scott  Blair, 

S.  R.  Bowen,  F.  S.  Brack,  H.  H.  Brix,  C.  A.  Canfield,  Frank  Cleary, 
H.  R.  Crozier,  F.  P.  Dagany,  P.  B.  Daubenspeck,  D.  M.  De  Long, 
J.  F.  Ecbert,  Andrew  Ferguson,  A.  D.  Ferguson,  W.  S.  Fisher,  A.  D. 
Fram,  Charles  Fredeman,  W.  M.  Graham,  W.  A.  Gray,  W.  A.  Greer, 
L.  P.  Guiberson,  H.  D.  Guthrey,  S.  H.  Hain,  H.  H.  Hart,  H.  Henshaw, 
W.  A.  Hersey,  Paul  Huntsch,  W.  A.  Irwin,  W.  H.  Kerr,  W.  P.  Kerr, 
J.  E.  Kibele,  Besley  Lafever,  J.  L.  Lennon,  M.  E.  Lombardi,  E.  W. 
Mason,  W.  G.  McCutcheon,  W.  O.  Miles,  J.  H.  Miller,  S.  E.  Mills,  R.  B. 
Moran,  T.  A.  O’Donnell,  P.  F.  Page,  R.  S.  Peeler,  Z.  L.  Phelps,  J.  H. 
Raney,  Charles  V.  Reynolds,  George  D.  Roberts,  C.  N.  Root,  Guy  H. 
Salisbury,  George  Schwinn,  Max  Shaffrath,  R.  E.  Shore,  R.  H.  Smith, 
H.  F.  Stranahan,  R.  E.  Thompson,  T.  H.  Turner,  J.  Waley,  J.  L.  D. 
Walp,  Alex  Wark,  J.  H.  Webb,  M.  L.  Woy,  J.  B.  Wrenn,  John  M. 
Wright,  and  many  others  who  have  contributed  in  one  way  or  another 
to  the  value  of  the  report. 

The  writers  also  wish  to  express  their  gratitude  to  R.  B.  Marshall, 
geographer  in  charge,  and  to  E.  P.  Davis,  topographer,  for  favors 
rendered  during  the  course  of  the  field  season,  when  the  topographic 
and  geologic  work  were  going  on  simultaneously. 

Advantage  of  cooperation  among  operators. — The  outlook  will  con- 
tinue to  be  bright  for  the  development  at  Coalinga  of  one  of  the 
greatest  fields  in  California  if  each  and  every  operator  will  conserve  to 
the  utmost  the  wonderful  supply  of  oil  stored  within  the  boundaries 
of  the  district,  and  by  wise  management  aid  in  keeping  it  available. 
The  amount  of  available  oil  in  the  territory  covered  by  the  under- 
ground-contour map  (PI.  II,  in  pocket)  is  estimated  at  2,825,000,000 
barrels.  Contrary  to  the  belief  of  some  people,  the  underground 
resources  of  the  earth  are  not  inexhaustible;  when  the  oil  in  any  field 


GEOGRAPHY  AND  TOPOGRAPHY. 


11 


is  once  gone  it  will  not  be  replaced  for  many  centuries,  if  ever.  It 
may  be  true  that  the  processes  of  oil  formation  and  migration  are  con- 
stantly taking  place  in  some  localities,  but  such  processes  are  so 
exceedingly  slow,  if  measured  in  years,  that  for  practical  purposes 
they  may  be  considered  as  having  ceased  altogether. 

Fortunately  the  Coalinga  field  has  had  little  of  the  serious  trouble 
with  water  that  is  ruining  certain  parts  of  some  of  the  other  fields  of 
California.  This  lack  of  trouble  is  probably  due  largely  to  the  little 
disturbed  condition  and  uniformity  of  the  oil  formations  over  most 
of  the  territory.  But  trouble  from  water  is  beginning  to  show  its 
effects  in  certain  parts  of  the  field,  and,  through  accident  or  care- 
lessness, some  wells  not  yet  abandoned  are  believed  to  be  letting  water 
into  sands  that  are  productive  in  not  far-distant  wells.  In  order  to 
avoid  the  dangers  incident  to  faulty  drilling  and  handling  of  wells, 
the  operators  should  meet  and  exchange  information  about  the  under- 
ground geology.  It  seems  shortsighted  for  one  operator  to  with- 
hold from  his  neighbor  his  logs  and  other  information  about  under- 
ground conditions,  when  this  very  withholding  may  be  the  cause  of 
his  neighbor’s  flooding  a large  area  through  lack  of  proper  knowledge 
in  shutting  off  the  water.  Furthermore,  it  is  hoped  that  those  in 
legislative  authority  will  recognize  the  needs  of  the  petroleum  inter- 
ests in  California,  and,  as  has  been  done  in  other  States,  provide  laws 
protecting  the  producers  from  negligent,  shortsighted,  or  criminally 
careless  operators. 

GEOGRAPHY  AND  TOPOGRAPHY. 

LOCATION. 

The  region  mapped  and  referred  to  in  this  report  as  the  Coalinga 
district  is  situated  in  the  southern  part  of  Fresno  County  and  the 
western  part  of  Kings  County,  Cal.,  and  is  bounded  on  the  south  by 
the  Kern  County  line.  It  forms  a long  strip  of  territory  extending 
from  119°  50'  west  longitude  and  35°  47'  north  latitude  at  its  south- 
east corner  to  120°  37'  west  longitude  and  36°  20'  north  latitude  at 
its  northwest  corner,  along  the  foot  of  the  Diablo  Range.  This  is 
the  easternmost  member  of  the  Coast  ranges  on  the  border  of  the  San 
Joaquin  Valley  of  California.  The  district  as  mapped  is  roughly  50 
miles  long  and  15  miles  wide  and  includes  about  700  square  miles. 
It  covers  the  foothill  belt  along  the  valley  and  extends  back  into  the 
high  hills  to  the  summits  of  the  first  surrounding  mountain  ridges,  its 
northwest  and  southwest  corners  reaching  to  the  crest  of  the  Diablo 
Range. 

The  developed  oil  territory  commonly  referred  to  as  the  Coalinga 
field  is  in  the  northern  part  of  the  district,  in  the  foothill  region 


12 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


around  Pleasant  Valley,  where  the  town  of  Coalinga  is  situated. 
This  is  the  only  important  settlement  in  the  district  or  in  a large  sur- 
rounding region,  the  country  being  very  sparsely  inhabited.  A rail- 
road line  connects  Coalinga  with  the  main  lines  of  the  Southern  Pacific 
and  the  Atchison,  Topeka  and  Santa  Fe  railroads  in  the  San  Joaquin 
Valley,  and  wagon  roads  enter  the  district  at  several  points  from  the 
valley  on  the  east.  Roads  cross  the  Diablo  Range  from  the  west  by 
four  routes,  (1)  over  the  Benito  Pass  at  the  head  of  Los  Gatos  Creek, 
(2)  over  the  divide  between  Priest  Valley  and  the  head  of  Waltham 
Creek,  (3)  across  the  range  between  Stone  Canyon  and  Waltham 
Creek,  and  (4)  over  Cottonwood  Pass.  The  first  enters  the  Coalinga 
district  along  Los  Gatos  Creek,  the  second  and  third  along  Waltham 
Creek,  and  the  fourth  through  McLure  Valley. 

DEFINITIONS  OF  PLACE  NAMES. 

It  is  important  that  the  names  of  the  various  places  and  features 
in  the  Coalinga  district  used  in  this  report  should  be  clearly  defined 
before  the  topographic  and  geologic  discussion  is  begun.  The  region 
is  one  in  which  little  detailed  investigation  has  been  made,  and  most 
of  the  natural  features  are  unnamed,  while  to  many  others  names  are 
indefinitely  applied.  The  following  definitions  of  names  that  have 
been  newly  applied  and  of  names  whose  application  has  been  made 
more  definite  have  been  submitted  to  the  United  States  Geographic 
Board  and  have  been  approved  and  made  permanent  by  that  body. 
Most  of  these  names  appear  on  the  map  (PL  I). 

Coalinga  district. — The  application  of  this  name  to  the  whole  region 
included  in  the  map  has  been  discussed  in  the  preceding  paragraphs. 

Coalinga  field. — The  term  field  has  been  adopted  as  representing  a 
subdivision  of  a district,  and  the  name  Coalinga  field  is  used  in  this 
report  in  its  accepted  sense  as  meaning  the  region  of  the  developed 
oil  field  in  the  northern  portion  of  the  territory  mapped,  round  about 
the  valley  (Pleasant  Valley)  in  which  Coalinga  is  situated.  This 
region  is  in  turn  subdivided  into  the  Eastside,  Westside,  and  Oil  City 
fields,  which  are  well  known  and  will  be  defined  later  (pp.  74-107). 

Kreyenhagen  field. — Similarly  the  region  of  the  hills  west  of  Kettle- 
man  Plain  is  referred  to  as  the  Kreyenhagen  field. 

Kettleman  Hills  field. — The  possible  future  oil  field  east  of  the  Ket- 
tleman  Plain  will  be  referred  to  as  the  Kettleman  Hills  field. 

Diablo  Range. — The  southern  limit  of  the  Diablo  Range  has  been 
fixed  at  Antelope  Valley  in  northwestern  Kern  County.  Heretofore 
the  name  has  been  used  indefinitely  for  part  or  all  of  the  easternmost 
members  of  the  Coast  Range  extending  southeastward  from  the  Car- 
quinez  Straits.  Antelope  Valley  is  fixed  as  the  southern  limit  of  the 
range  because  the  mountains  there  sink  into  low  spurs,  and  the  con- 
tinuation of  the  mountain  belt  beyond  is  a markedly  individual  range 


GEOGRAPHY  AND  TOPOGRAPHY. 


13 


that  is  en  echelon  with  Avenal  Ridge,  between  Antelope  and  McLure 
valleys,  which  is  the  southernmost  spur  of  the  Diablo  Range.  The 
United  States  Geographic  Board  has  determined  that  the  correct 
name  is  Diablo  Range,  instead  of  Mount  Diablo,  Monte  Diablo,  or 
Sierra  del  Monte  Diablo. 

Temblor  Range. — Southeast  of  Antelope  Valley  a range  of  distinct 
topographic  and  structural  individuality  forms  the  divide  between  the 
San  Joaquin  Valley  on  the  northeast  and  the  basin  of  San  Juan  Creek 
and  the  Carrizo  Plain  on  the  southwest.  It  extends  from  Cholame 
Creek  on  the  north  to  about  latitude  35°,  where  it  merges  with  the 
high  mountain  mass  around  Mount  Pinos  called  the  Tejon  Mountains. 
To  this  range  the  name  Temblor  is  here  applied.  This  name,  which 
is  Spanish  for  earthquake,  is  particularly  suited  to  the  range  for  two 
reasons.  First,  because  the  great  California  fault  line,  along  which 
earthquakes  have  repeatedly  originated,  follows  the  range  from  one 
end  to  the  other,  being  in  the  very  heart  of  it  throughout  its  northern 
part.  A pronounced  scarp  resulting  from  the  movement  in  1868  can 
still  be  traced  for  much  of  the  distance  along  this  line.  Second, 
because  the  well-known  old  Temblor  ranch,  west  of  McKittrick,  is 
situated  on  its  flanks. 

Joaquin  Ridge. — A very  prominent  structural  ridge,  here  named 
Joaquin  Ridge,  runs  east-southeast  from  the  high  mountains  south  of 
San  Carlos  Peak  to  the  San  Joaquin  Valley  north  of  Coalinga,  forming 
the  divide  between  Los  Gatos  Creek  on  the  south  and  tributaries  of 
Salt  Creek  and  Cantua  Creek  that  run  northeastward  to  the  San 
Joaquin  Valley.  The  ridge  heads  at  a mountain  almost  5,000  feet 
high,  situated  in  the  southeastern  portion  of  T.  18  S.,  R.  12  E.,  in  the 
northeast  corner  of  the  area  mapped,  on  the  divide  between  the 
tributaries  of  Los  Gatos  Creek  and  San  Benito  River.  Its  summit 
is  serrated  with  picturesque  rocks,  one  striking  group  of  which  is 
locally  known  as  the  Joaquin  Rocks.  The  oil  field  north  of  Coalinga 
lies  on  the  nose-  of  this  ridge. 

Anticline  Ridge. — Southeast  of  a depression  in  the  Joaquin  Ridge  in 
the  southern  part  of  sec.  34,  T.  19  S.,  R.  15  E.,  a low  broad  line  of 
hills  extends  about  6 miles  to  the  railroad  line  in  the  gap  formed  by 
Los  Gatos  Creek.  This  ridge  is  formed  by  a perfect  anticlinal  nose 
and  is  therefore  referred  to  as  Anticline  Ridge. 

Juniper  Ridge. — A corresponding  and  approximately  parallel  ridge 
runs  south  of  Los  Gatos  Creek  from  the  divide  between  that  stream 
and  Lewis  Creek  as  far  as  the  canyon  of  Waltham  Creek  (Alcalde  Can- 
yon). It  is  a high,  rugged  ridge  separating  the  important  Waltham 
Valley  depression  on  the  southwest  from  the  Los  Gatos  Creek  depres- 
sion on  the  northeast  and  from  the  low  hills  between  Los  Gatos  and 
Waltham  creeks  (Alcalde  Hills)  on  the  east.  It  is  cut  abruptly  by 
Waltham  Creek,  south  of  which  it  is  continued  for  about  2 miles  in 


14 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


the  isolated  ridge  known  as  Curry  Mountain.  It  is  here  called  Juni- 
per Ridge  owing  to  its  characteristic  vegetation. 

Avenal  Ridge. — The  name  Avenal  Ridge  is  here  applied  to  the 
mountains  separating  Avenal  Creek  and  McLure  Valley  from  the  Cho- 
lame  and  Antelope  valleys.  It  is  the  southernmost  of  the  spurs  of  the 
Diablo  Range.  The  name,  which  means  a field  of  oats,  is  appropriate 
because  the  hills  forming  the  ridge  are  rounded  and  grass  grown. 

Reef  Ridge. — A prominent  escarpment  faces  the  low  hills  that  border 
the  Kettleman  Plain,  running  southeastward  from  the  southern  fork 
of  Jacalitos  Creek  (Jasper  Canyon)  as  far  as  Little  Tar  Canyon,  north 
of  Dudley.  This  is  formed  by  the  prominent  lower  Miocene  fossilif- 
erous  strata  termed  the  “Reef  beds,”  which  dip  at  a high  angle  and, 
owing  to  their  resistance  to  erosion,  rise  high  above  the  softer  sand 
hills  on  the  northeast.  This  escarpment  forms  the  northeastern  flank 
of  a ridge  to  which  the  name  Reef  Ridge  is  here  applied.  The  name  is 
expressive  of  its  prominent  topographic  character. 

Alcalde  Hills. — The  foothills  between  Los  Gatos  and  Waltham 
creeks,  east  of  Juniper  Ridge,  northwest  of  Alcalde  and  west  of  Coa- 
linga  are  here  called  the  Alcalde  Hills. 

Jacalitos  Hills. — The  foothills  between  Waltham  and  Jacalitos 
creeks  are  here  called  the  Jacalitos  Hills.  Xacalli  is  an  Aztec  word 
adopted  by  the  Mexicans,  meaning  Indian  hut  or  wigwam,  and  Jaca- 
litos means  the  little  wigwams. 

Kreyenhagen  Hills. — The  foothills  southeast  of  Jacalitos  Creek  be- 
tween Reef  Ridge  and  Kettleman  Plain  may  be  named  Kreyenhagen 
Hills.  The  name  is  that  of  three  families  owning  large  tracts  of  land 
there.  They  are  early  settlers  and  practically  the  only  inhabitants, 
and  the  region  is  generally  known  as  the  Kreyenhagen  country  or 
Kreyenhagen’s.  Kreyenhagen  field  is  the  name  used  in  this  report 
for  the  oil  field  of  the  vicinity. 

Pyramid  Hills. — A long  narrow  line  of  hills  borders  the  eastern  side 
of  McLure  Valley,  extending  from  Little  Tar  Canyon  about  3 miles 
north  of  Dudley  to  the  gap  (Dagany  Gap)  where  the  Avenal  flows  out 
of  the  valley  about  4 miles  south  of  Dudley;  south  of  this  gap  they 
continue  into  the  Devils  Den  region.  They  form  a ridge  capped  by 
a succession  of  conical  hills,  which  when  viewed  from  the  east  appear 
like  isolated  pyramids,  and  are  therefore  here  called  the  Pyramid 
Hills. 

Tent  Hills. — A somewhat  similar  line  of  hills  of  peculiar  topographic 
and  geologic  structure  extends  along  the  Avenal  at  the  northeastern 
foot  of  the  high  ridge  (Avenal  Ridge)  west  of  McLure  Valley.  They 
begin  about  4 miles  west  of  Dudley  and  run  3J  miles  northwest,  being 
separated  from  Avenal  Ridge  by  a marked  depression.  Owing  to  the 
resemblance  of  the  individual  hills  to  tents  they  are  here  called  the 
Tent  Hills, 


GEOGRAPHY  AND  TOPOGRAPHY. 


15 


Guijarral  Hills. — Immediately  southeast  of  Anticline  Ridge,  on  the 
opposite  side  of  the  railroad,  is  a small  low  group  of  gravelly  hills 
referred  to  in  the  text  as  the  Guijarral  Hills.  The  word  is  Spanish 
and  means  a heap  of  pebbles  or  a place  abounding  in  pebbles. 

Dagany  Gap. — The  name  Dagany  Gap  is  used  for  the  gap  at  the 
lower  end  of  the  McLure  Valley  south  of  Dudley.  It  is  named  from 
an  old  settler  of  that  region. 

Avenal  Gajp. — The  Kettleman  Hills  are  cut  at  latitude  35°  50'  by  a 
completely  graded  stream  channel  now  followed  by  Avenal  Creek.  It 
will  be  referred  to  as  Avenal  Gap. 

Polvadero  Gap. — At  their  northern  end  the  Kettleman  Hills  are 
separated  from  the  Guijarral  Hills  by  a gap  through  which  flow  Zapato 
and  Canoas  creeks.  It  is  called  Polvadero  Gap  because  it  is  subject  to 
dust  storms.  Certain  of  the  early  land  maps  have  it  Pulvero,  but 
this  is  not  correct. 

Pleasant  Valley. — At  least  a portion  of  the  valley  at  the  mouth  of 
Los  Gatos  Creek  has  been  known  as  Pleasant  Valley,  the  usage  not 
being  definite.  The  name  may  well  be  applied  to  the  whole  basin  in 
which  Coalinga  is  situated. 

Waltham  Valley  and  Creek  and  Alcalde  Canyon. — The  creek  at  the 
mouth  of  which  Alcalde  is  situated  is  variously  known  as  Wartham, 
Warthan,  Waltham,  and  Alcalde.  The  United  States  Geographic 
Board  has  decided  that  Waltham  is  the  correct  name.  This  stream 
heads  in  a broad  structural  valley  having  no  relationship  in  geologic 
character  with  the  canyon  through  which  it  flows  lower  down.  The 
name  Waltham  Valley,  already  in  use  for  this  upper  valley,  should  be 
restricted  definitely  to  it  and  not  applied  to  the  lower  canyon,  which 
it  seems  advisable  to  distinguish  under  the  name  Alcalde  Canyon,  thus 
preserving  a name  which  is  already  understood  as  referring  only  to  the 
lower  part.  This  name  is  therefore  applied  to  the  canyon  extending 
from  the  edge  of  Waltham  Valley,  where  the  stream  cuts  between 
Juniper  Ridge  and  Curry  Mountain,  to  Pleasant  Valley.  The  stream 
itself  bears  the  same  name  throughout. 

McLure  Valley. — The  valley  in  which  Dudley  is  situated  has  long 
been  known  as  McLure  Valley,  after  an  early  settler,  now  dead. 
According  to  old  inhabitants  this  is  the  original  and  proper  name. 
It  is  widely  known  also  as  Sunflower  Valley,  by  reason  of  the  abun- 
dant growth  within  it  of  wild  sunflowers.  The  United  States  Geo- 
graphic Board  has  decided  that  the  former  is  the  correct  name. 

Kettleman  Hills  and  Plain. — The  United  States  Geographic  Board 
has  decided  that  the  name  applied  to  these  features  should  be  written 
with  an  “ e”  and  should  not  be  spelled  Kittleman. 

Various  creeks  and  canyons. — The  United  States  Geographic  Board 
has  considered  the  various  usages  in  regard  to  the  names  of  the 


16 


COALING  A OIL  DISTRICT,  CALIFORNIA. 


creeks  in  the  Coalinga  district,  and  the  results  of  its  decisions  appear 
on  the  map  (PL  I,  in  pocket). 

For  convenience  of  reference  the  authors  have  applied  names  to 
several  canyons  in  the  district.  The  one  which  runs  north  and  south 
7 to  10  miles  due  north  of  Coalinga,  and  which  is  followed  by  the  road 
to  Oil  City,  is  named  Oil  Canyon.  The  one  in  the  Alcalde  Hills 
which  runs  southeastward  across  sections  2,  11,  12,  and  13,  T.  21  S., 
R.  14  E.,  and  which  throughout  its  course  across  sections  2,  11,  and 
12  is  practically  coincident  with  an  anticline,  is  called  Anticline 
Canyon. 

The  application  of  the  name  Alcalde  Canyon  has  been  shown  above. 
The  southern  fork  of  Jacalitos  Creek  may  be  appropriately  named 
Jasper  Creek  from  the  picturesque  and  brilliant  colored  buttes  of 
jasper  that  surround  its  upper  portion,  and  the  name  Jasper  Canyon 
is  therefore  applied  to  the  gorge  cut  by  this  stream  across  the  north- 
west end  of  Reef  Ridge.  The  sharp  canyon  cut  through  Reef  Ridge 
by  Zapato  Creek  is  called  Zapato  Canyon,  and  the  similar  one  formed 
through  Reef  Ridge  by  the  southern  fork  of  Zapato  Creek  2 miles 
farther  east  may  be  named  Sulphur  Spring  Canyon,  from  the  abun- 
dance of  sulphur  water  that  issues  in  it.  The  similar  canyon  at  the 
head  of  Canoas  Creek  is  called  Canoas  Canyon.  The  names  Big  Tar 
Canyon  and  Little  Tar  Canyon  are  in  common  use  for  the  features 
to  which  these  names  are  applied  on  the  map. 

Laval  grade. — The  Laval  grade  is  a name  locally  known  for  the 
road  leading  northeastward  up  a branch  of  Oil  Canyon,  starting  in 
that  canyon  on  the  eastern  side  of  the  NW.  J sec.  29,  and  crossing 
the  ridge  at  the  head  of  this  branch  canyon  in  the  center  of  the  NW.  J 
sec.  21,  T.  19  S.,  R.  15  E. 

GENERAL  TOPOGRAPHIC  FEATURES. 

The  Coalinga  district  owes  its  broader  topographic  features  to  its 
position  along  the  border  between  the  Coast  Range  and  the  San 
Joaquin  Valley.  It  is  largely  a region  of  foothills  that  rise  on  the 
west  into  the  mountains  and  merge  on  the  east  with  the  wide  level 
plain.  The  foothills  form  several  groups  around  the  base  of  spurs 
descending  southeastward  from  the  Diablo  Range,  the  groups  being 
separated  from  each  other  by  reentrant  valleys  that  open  out  to  the 
San  Joaquin  Valley. 

The  Diablo  Range  in  this  latitude  is  a rugged  mountain  group 
made  up  of  various  component  members,  some  of  which,  owing  to  a 
complication  of  structures,  run  at  angles  oblique  to  the  main  trend 
of  the  range  northwest  and  southeast.  The  crest  of  the  range  has  a 
general  altitude  varying  between  2,500  and  5,000  feet,  and  declines 
in  height  from  the  region  northwest  of  the  Coalinga  district  toward 
the  region  southwest  of  it,  where  it  has  been  assumed  as  coming  to  a 


GEOGRAPHY  A.ND  TOPOGRAPHY. 


17 


stop  and  giving  place  on  the  southwest  to  the  Temblor  Range.  Por- 
tions of  the  watershed  appear  upon  the  map  (PL  I)  at  only  two 
points,  viz,  in  the  northwest  corner,  which  is  marked  by  a peak 
nearly  5,000  feet  high  that  stands  at  the  head  of  Joaquin  Ridge;  and 
in  the  southwest  corner,  where  the  much  lower  Avenal  Ridge,  the 
southernmost  spur  of  the  range,  appears.  In  the  intermediate  region 
the  ridges  that  are  represented  on  the  edge  of  the  map  are  in  general 
separated  from  the  main  divide  of  the  range  by  a region  of  lower 
relief  determined  by  the  presence  of  transverse  structural  valleys,  of 
which  Waltham  Valley  is  the  principal  example.  The  general  topo- 
graphic development  is  youthful,  but  there  is  evidence  in  certain 
localities  of  different  stages  of  development  up  to  advanced  youth. 
A feature  of  the  relief  of  the  whole  region  is  the  topographic  reflection 
of  the  geologic  structure,  a feature  that  is  especially  pronounced  in 
the  foothills  belt,  with  which  this  report  particularly  deals. 

A peculiar  feature  of  the  Diablo  Range  is  the  occurrence  along  its 
eastern  flanks  of  many  spurs  running  out  toward  the  southeast,  and 
of  reentrant  valleys  between  these  spurs.  These  ridges  and  valleys 
have  an  orientation  slightly  more  to  the  east  and  west  than  that  of 
the  whole  range,  which  trends  in  general  about  N . 36°  to  40°  W.  and 
S.  35°  to  40°  E.  They  are  primarily  due  to  structural  causes  and 
not  to  erosion.  The  main  salients  of  the  Diablo  Range  that  project 
toward  the  San  Joaquin  Valley  in  the  Coalinga  district  are  Joaquin 
Ridge  and  the  Kettleman  Hills,  Juniper  Ridge  and  Curry  Mountain, 
Reef  Ridge,  the  high  hills  northwest  of  McLure  Valley  between  the 
drainage  of  Big  Tar  Canyon  and  Avenal  Creek,  and  Avenal  Ridge. 
These  and  the  valleys  or  depressions  separating  them  are  the  topo- 
graphic expression  of  structural  features  running  transverse  to  the 
main  trend  of  the  Diablo  Range  and  are  en  echelon  with  each  other. 

Joaquin  Ridge  is  anticlinal  and  exposes  on  its  lower  flanks  the  oil- 
bearing formations,  thus  determining  the  position  of  the  oil  field  north 
of  Coalinga.  The  ridge  is  structurally  continued  by  the  Kettleman 
Hills,  which  form  a prominent  isolated  group  rising  over  1,000  feet 
above  the  San  Joaquin  Valley.  The  spur  formed  by  Joaquin  Ridge 
and  the  Kettleman  Hills  is  separated  from  the  rest  of  the  district  by 
the  synclinal  and  faulted  depression  of  White  and  Los  Gatos  creeks 
and  the  synclinal  Pleasant  Valley  and  Kettleman  Plain.  The  two 
latter  form  a continuous,  almost  level,  graded  plain,  opening  only 
locally  into  the  San  Joaquin  Valley  through  narrow  gaps  formed  by 
graded  stream  channels. 

Juniper  Ridge  and  Curry  Mountain,  southeast  of  the  Los  Gatos 
Creek  and  Pleasant  Valley  depression,  form  a continuous  structural 
feature  probably  due  to  faulting  on  the  southwest  side.  In  the  south- 
eastern portion  of  this  spur  it  presents  a steep  scarp  on  the  southwest 
52332— Bull.  357—08 2 


18 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


bounding  Waltham  Valley,  and  on  the  northeast  a gradual  mono- 
clinal  slope  into  the  Alcalde  Hills.  The  end  of  Curry  Mountain  drops 
abruptly  into  a depressed  area  of  low  rolling  hills  (the  Jacalitos  Hills) 
that  is  the  continuation  southeastward  of  the  Waltham  Valley  depres- 
sion. Beyond  this  area  a prominent  salient  springs  up  along  Jacalitos 
Creek  and  extends  southeastward  as  a high  divide  between  the  belt 
of  lower  relief,  in  which  Jacalitos,  Zapato,  Canoas,  and  Big  Tar  creeks 
head,  and  the  foothills  bordering  the  Kettleman  Plain.  This  divide 
is  Reef  Ridge,  and  all  the  streams  named,  as  well  as  their  forks,  cut 
deep  gorges  through  it.  The  ridge  has  a general  monoclinal  struc- 
ture, the  component  strata  dipping  steeply  northeastward  into  the 
foothills.  The  ridge  is  due,  in  large  part  at  least,  to  the  resistant 
qualities  of  the  Vaqueros  and  Tejon  strata  forming  its  crest.  At  its 
southeastern  extremity  it  gives  place  to  the  minor  ridge  of  the  Pyra- 
mid Hills,  which  is  en  echelon  with  it. 

The  next  important  salient  enters  the  area  shown  on  the  map  at  a 
point  south  of  the  head  of  Big  Tar  Canyon  and  the  Castle  Mountain 
fault  zone.  It  is  a high  and  prominent  group  of  hills  forming  the 
eastward  continuation  and  the  end  of  the  precipitous  ridge  of  Castle 
Mountain.  Reef  Ridge  and  the  last-mentioned  hills  are  separated 
from  the  next  salient  to  the  south  by  the  wide  plain  of  McLure 
Valley  and  by  the  valley  of  Avenal  Creek.  This  depression  is  com- 
parable in  structure  and  size  with  Pleasant  Valley.  Southwest  of 
McLure  Valley  rises  Avenal  Ridge,  the  main  divide  of  the  Diablo 
Range.  It  is  formed  by  an  important  closely  folded  anticline  that 
plunges  steeply  southeastward  and  brings  the  range  to  an  end.  Still 
farther  southwest,  on  the  opposite  flank  of  Avenal  Ridge,  extends  the 
large  Antelope  Valley,  which  is  of  the  same  peculiar  structural  type 
as  the  valleys  already  mentioned. 

The  foothills  that  swing  around  the  bases  of  these  spurs  of  the 
Diablo  Range  form  a rolling  surface  that  descends  gradually  to  the 
surrounding  plains.  They  owe  their  form  chiefly  to  three  causes: 
(1)  The  general  reflection,  on  the  surface,  of  the  folds  to  which  their 
uplift  is  due;  (2)  erosion  along  lines  directed  down  the  slope  toward 
the  valleys,  at  right  angles  to  the  structural  lines,  as  a result  of  which 
a series  of  lateral  ridges  is  formed;  and  (3)  erosion  along  structural 
lines,  particularly  along  bedding  planes  and  lines  of  contact,  as  a 
result  of  which  parallel  longitudinal  ridges  and  valleys  and  rows  of 
hills  are  formed,  and  the  lateral  ridges  deformed  or  dissected  into 
hills.  The  succession  of  longitudinal  ridges  and  intervening  sym- 
metrical troughs,  to  which  the  name  Canoas,  meaning  canoes,  prob- 
ably refers,  is  a particularly  striking  feature  of  the  Jacalitos  and 
Kreyenhagen  hills.  Further  detailed  sculpturing  is  due  to  erosional 
wash  along  small  channels  tributary  and  at  right  angles  or  oblique  to 


GEOLOGY. 


19 


the  streams  determined  by  these  two  main  factors.  The  soft  for- 
mations of  which  the  hills  are  largely  composed  lend  themselves  to 
minute,  rapid,  and  fairly  uniform  sculpturing,  which  gives  the  hills 
a wrinkled  appearance,  especially  evident  when  the  rays  of  the  sun, 
falling  obliquely,  cause  an  intricate  scattering  of  light  and  shade.  A 
general  similarity  of  elevations  is  characteristic  of  the  foothill  areas, 
which,  as  a rule,  show  comparatively  slight  relative  relief. 

The  two  most  important  streams  of  the  district  are  Los  Gatos  and 
Waltham  creeks,  which  drain  considerable  areas  and  flow  through 
deep,  structurally  important,  and,  in  their  lower  portion,  nearly 
graded  valleys.  These  streams  join  in  Pleasant  Valley  and  pass  out 
to  the  San  Joaquin  Plain  through  a gap  cut  across  the  uplift  of  the 
Coalinga  anticline.  The  deep  sharp  canyon  cut  by  Waltham  Creek 
through  Juniper  Ridge  and  Curry  Mountain  and  thence  eastward  for 
over  3 miles  to  Alcalde  is  worthy  of  remark.  Other  important 
streams  are  Jacalitos,  Zapato,  and  Avenal  creeks,  of  which  much  the 
same  can  be  said,  except  that  the  origin  of  the  lower  courses  of  the 
former  two  is  not  so  much  due  to  structure  as  is  that  of  the  others 
mentioned.  All  of  these  are  antecedent  to  the  latest  structural 
movements  and  form  sharp  cuts  across  features  that  have  been  up- 
lifted in  their  path  during  Quaternary  time.  Owing  to  the  slight 
rainfall  in  this  region  and  the  prolonged  drought  in  summer  none  of 
these  streams  carries  much  water,  and  they  all  become  nearly  dry 
during  the  dry  season. 

Tulare  Lake  borders  the  southeastern  portion  of  the  Coalinga  dis- 
trict east  of  the  Kettleman  Hills.  It  is  broad  and  shallow,  occupying 
a portion  of  the  almost  level  floor  of  the  San  Joaquin  Valley.  It  is 
supplied  with  water  by  several  rivers  descending  the  Sierra  Nevada 
and  has  no  outlet.  Owing  to  unusual  precipitation  during  1907  it 
extended  its  borders  widely,  reaching  nearly  to  the  base  of  the 
Kettleman  Hills.  During  preceding  years  the  lake  had  been  drying 
up  and  had  almost  ceased  to  exist.  Its  border  as  shown  on  PL  I, 
therefore,  represents  an  abnormally  extended  position. 

GEOLOGY. 

GENERAL  STATEMENT. 

♦ 

The  eastern  slope  of  the  mountains  bordering  the  San  Joaquin 
Valley  is  formed  by  a great  thickness  of  strata  dipping  toward  the 
valley.  The  oldest  rocks  exposed  appear  in  the  axis  of  the  mountain 
range  at  the  base  of  the  monocline,  successively  younger  formations 
appearing  eastward  as  the  edge  of  the  valley  is  approached.  The 
different  formations  that  may  be  recognized  as  units  in  this  series, 
with  the  time  divisions  to  which  they  correspond,  are  as  follows, 


20 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


from  the  oldest  to  the  youngest:  Franciscan  (Jurassic?),  Knoxville 
(lower  Cretaceous),  Chico  (upper  Cretaceous),  Tejon  (Eocene), 
Vaqueros  (lower  Miocene),  Santa  Margarita  (upper  middle  Miocene), 
Jacalitos  (early  upper  Miocene),  Etchegoin  (uppermost  Miocene), 
Paso  Robles  (Pliocene  and  early  Pleistocene),  and  late  Quaternary 
alluvium  and  terrace  deposits.  These  formations,  with  the  exception 
of  certain  igneous  and  metamorphic  rocks  associated  with  the  Fran- 
ciscan, are  of  sedimentary  origin,  the  sediments  being  marine,  with 
the  exception  of  moM  of  the  Paso  Robles  and  later  deposits.  They 
indicate  that  the  greater  portion  of  the  area  included  within  the 
Coalinga  district  was  beneath  the  sea  during  intervals  occupying 
probably  the  major  portion  of  the  time  from  the  Jurassic  to  the  end 
of  the  Miocene.  The  latest  movements  of  the  land,  which  produced 
the  features  of  topographic  relief  now  to  be  seen,  did  not  take  place 
until  within  Quaternary  time. 

The  first  three  of  the  above  formations  are  of  little  importance  in 
this  district  in  connection  with  the  occurrence  of  petroleum.  The 
Tejon  and  Vaqueros  are  the  principal  reservoirs  of  the  oil,  and  are 
therefore  of  prime  importance.  The  Santa  Margarita  and  Jacalitos 
are  petroliferous  only  at  their  bases,  and  their  upper  beds,  together 
with  those  of  the  Etchegoin,  are  the  strata  which  overlie  the  oil  sands 
and  through  which  the  wells  are  drilled,  so  that  their  relation,  thick- 
ness, character,  and  structure  have  an  important  bearing  on  the 
problem  of  accessibility  of  the  oil  and  are  worthy  of  detailed  study. 
The  Paso  Robles  formation  is  of  less  direct  importance  in  this  con- 
nection, but  is  of  aid  in  throwing  light  on  the  structure  and  the  rela- 
tions of  the  different  formations. 

STRATIGRAPHY. 

FRANCISCAN  FORMATION  (JURASSIC?). 

General  description. — The  central  portion  of  the  Diablo  Range  is 
occupied  by  an  old  and  for  the  most  part  much-altered  formation 
that  is  in  every  way  similar  to  the  well-known  Franciscan  formation 
of  other  parts  of  the  State.  It  comprises  the  oldest  rocks  here  ex- 
posed, as  it  antedates  the  Knoxville  (Lower  Cretaceous),  but  further 
than  this  little  can  be  said  regarding  its  age.  It  is  usually  considered 
Jurassic,  but  elsewhere  there  is  no  good  fossil  evidence  of  its  age, 
and  in  this  region  none  has  been  found. 

The  Franciscan  is  easily  recognizable,  as  it  is  characterized  by 
typical  rocks  and  topography.  The  most  characteristic  feature  of 
the  areas  occupied  by  the  Franciscan  is  the  serpentine,  which  is  every- 
where associated  with  it  and  which  is  here  considered  a part  of  it, 
although  in  reality  intrusive  in  the  sedimentary  rocks,  and  therefore 
of  later  age.  The  original  sedimentary  rocks,  which  are  sandstone, 


GEOLOGY. 


21 


shale,  and  jasper,  occur  in  detached  areas  and  are  greatly  disturbed. 
They  are  intimately  associated  with  glaucophane,  actinolite,  and 
other  schists;  serpentine,  and  other  metamorphic  rocks;  and  in  one 
area  shown  on  the  map  with  soda-bearing  hornblende  syenite.  In 
the  portion  of  the  Coast  Range  within  and  bordering  the  Coalinga 
district  the  metamorphic  rocks  of  the  Franciscan  formation  greatly 
predominate  over  the  unaltered  ones.  In  the  small  area  of  Franciscan 
sedimentary  beds  in  the  northwest  corner  of  the  district,  the  alter- 
nating beds  of  sandstone  and  shale  closely  resemble  the  strata  in  the 
lower  portion  of  the  Knoxville-Chico  and  are  difficult  to  separate 
from  them.  The  serpentine  covers  a much  larger  area  and  extends 
far  beyond  the  limits  shown  on  the  map  over  a continuous  stretch 
estimated  as  being  at  least  40  square  miles.  The  Franciscan  forma- 
tion and  associated  rocks  are  considerably  mineralized  and  contain 
deposits  of  cinnabar,  asbestos,  and  the  newly  described  gem  mineral, 
benitoite.® 

Importance  with  relation  to  petroleum. — The  rocks  of  the  Franciscan 
are  not  known  to  contain  any  petroleum.  The  formation  is  of  dif- 
ferent character  from  the  formations  in  which  the  oil  is  found  and 
has  no  direct  relation  to  them.  Even  if  it' had  once  been  a source  of 
petroleum,  the  disturbance  that  it  has  undergone  could  have  allowed 
little  to  remain. 

KNOXVILLE-CHICO  ROCKS  (CRETACEOUS). 

General  description. — The  next  oldest  rocks  exposed  in  the  Coalinga 
district  comprise  a thick  series  of  strata  of  sandstone,  shale,  and  con- 
glomerate overlying  with  probable  unconformity  the  Franciscan 
formation  just  described,  and  covering  a wide  belt  for  the  most  part 
west  of  the  foothill  region.  They  form  the  high  hills  north  and 
south  of  Los  Gatos  and  Waltham  creeks  and  may  be  easily  recognized 
by  the  dark,  thin-bedded,  compact  shale  and  sandstone  of  the  lower 
portion  and  the  massive,  drab,  concretionary  sandstone  of  the  upper 
portion.  These  rocks  are  of  Cretaceous  age  and  comprise  part  or  all 
of  the  two  formations  well  known  elsewhere  on  the  west  coast  as 
Knoxville  (lower  Cretaceous)  and  Chico  (upper  Cretaceous).  Owing 
to  the  lack  of  fossil  or  stratigraphic  evidence  in  the  Coalinga  district 
sufficient  to  form  the  basis  for  a separation  between  these  two  forma- 
tions, they  are  mapped  and  described  together  for  the  present. 

The  rocks,  however,  may  be  separated  lithologically  into  three 
divisions.  A marked  distinction  between  the  lower  and  upper  por- 
tions has  already  been  noted,  but  the  thin-bedded  shale  and  sand- 
stone making  up  the  lower  portion  is  divided  into  two  parts  by  a 

a Louder  back,  G.  D.,  Benitoite,  a new  California  gem  mineral,  with  chemical  analyses  by  W.  C.  Bias- 
dale:  Bull.  Dept.  Geol.  Univ.  California,  vol.  5,  No.  9,  July,  1907.  pp.  149-153.  Also,  Arnold,  Ralph, 
Notes  on  the  occurrence  of  the  recently  described  gem  mineral  benitoite:  Science,  new  ser.,  vol.  27, 
No.  686,  February  21,  1908,  pp.  312-314. 


22 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


conformably  interbedded  zone  of  coarser  sediments  and  in  places  by 
several  hundred  feet  of  coarse  massive  conglomerate,  as  along  Alcalde 
Canyon  and  on  Juniper  Ridge. 

The  beds  above  and  below  the  conglomerate  zone  are  of  the  same 
character,  predominantly  dark  argillaceous  shale  in  thin  layers  with 
partings  of  sandstone,  but  it  is  possible  that  the  conglomerate  zone 
represents  an  important  stratigraphic  separation.  Chico  (upper 
Cretaceous)  fossils  have  been  found  north  of  White  Creek  and  near 
Alcalde  in  the  shale  series  at  horizons  higher  than  the  conglomerate, 
and  it  is  possible  that  the  zone  of  coarsening  in  the  sediments  repre- 
sents the  base  of  the  Chico.  The  beds  below  the  conglomerate  are 
at  least  3,000  feet  thick,  and  probably  belong  to  the  Knoxville  (lower 
Cretaceous).  Fossils  of  this  age  have  been  found  in  similar  beds  in 
the  Devils  Den  region,  not  far  south  of  the  area  mapped.  The  strata 
of  the  middle  division,  above  the  base  of  the  conglomerate,  have  a 
thickness  of  at  least  4,800  feet. 

The  uppermost  of  the  three  divisions  is  predominantly  sandstone, 
and  has  a thickness  of  at  least  3,500  feet.  The  sandstone  is  usually 
of  a drab  color,  medium  grained,  and  not  very  hard.  It  occurs  in 
massive  beds,  often  weathering  cavernous,  that  stand  out  promi- 
nently and  display  the  structure  on  the  sides  and  tops  of  the  ridges 
north  of  Los  Gatos  Creek  and  west  of  Coalinga.  Rocks  of  this  divi- 
sion may  be  easily  recognized  by  these  characteristic  outcrops  and 
by  the  numerous  large,  hard,  reddish-brown  concretions  of  which  the 
sandstone  is  full  and  which  weather  out  and  remain  in  patches  on 
the  surface.  The  beds  are  in  places  so  concretionary  that  the  indi- 
vidual oval  concretions  lose  their  identity  and  the  beds  are  composed 
throughout  of  hard  brown  rock  like  that  forming  the  concretions. 
The  prominent  sandstone  strata  are  separated  by  poorly  exposed, 
softer  beds  of  sand  and  light-colored  shale.  Locally  the  sandstone  is 
conglomeratic.  Thin  seams  of  calcareous  shale  and  sand  are  at  some 
points  interbedded  with  the  softer  beds.  At  the  base  of  this  division 
of  the  Knoxville-Chico  rocks,  the  massive  sandstone  beds  give  place 
to  thinner  beds  alternating  with  finer-grained  sandstone  and  shale, 
and  these  grade  over  into  the  thin-bedded  series  described  as  the 
middle  division.  The  transition  takes  place  within  a few  hundred 
feet,  and  in  places  a fairly  sharp  line  can  be  traced  between  the  beds 
that  are  predominantly  sandstone  and  those  in  which  the  thin  layers 
of  fine  grain  predominate.  Fossils  of  Chico  (upper  Cretaceous)  age 
occur  at  various  localities  in  sandstone  and  conglomerate  in  the  lower 
portion  of  this  upper  division;  the  upper  portion  has  not  furnished 
fossils  and  can  be  only  doubtfully  referred  to  the  Chico  formation. 
The  upper  part  of  the  concretionary  sandstone  series  may  be  either 
Chico  or  Tejon  (Eocene),  or  a transition  between  these  two  forma- 
tions. The  division  is,  however,  fairly  homogeneous  in  character  and 


GEOLOGY. 


28 


seems  to  represent  a separate  stratigraphic  unit,  and  it  is  therefore, 
for  the  time  being  at  least,  referred  as  a whole  to  the  Chico  formation; 
considered  as  such,  it  is  strikingly  distinct  from  the  divisions  below 
and  from  other  formations  in  the  district. 

Importance  with  relation  to  petroleum. — The  Knoxville-Chic o strata 
are  not  petroleum  bearing  so  far  as  known.  It  is  possible  that  traces 
of  oil  may  be  found  in  them,  but  there  is  nothing  to  indicate  that 
they  contain  it  in  quantity  sufficient  to  be  of  economic  importance. 
The  beds  underlie  the  Tejon  (Eocene)  formation,  in  which  the  petro- 
leum of  the  Coalinga  district  is  supposed  to  have  originated,  and 
below  which  no  petroleum  has  been  found. 

TEJON  FORMATION  (EOCENE). 

General  description. — The  beds  of  the  Knoxville-Chico  are  overlain 
unconformably  by  beds  belonging  to  the  Tejon  (Eocene)  formation. 
This  is  a marine  sedimentary  formation,  which  was  named  from  the 
locality  near  Fort  Tejon  in  Kern  County,  where  it  occurs  typically. 
It  forms  a belt  along  the  western  edge  of  the  San  Joaquin  Valley 
and  is  exposed  intermittently  in  the  region  between  the  type  locality 
and  the  Coalinga  district.  No  sharp  line  of  demarcation  is  to  be 
drawn  between  the  Tejon  and  the  underlying  Chico  in  the  northern 
part  of  the  district,  and  in  places  there  appears  to  be  a gradation 
from  the  beds  of  the  former  into  those  of  the  latter,  as  if  they  had 
been  formed  during  a continuous  period  of  sedimentation. 

The  Tejon  formation  in  the  Coalinga  district  is  made  up  entirely 
of  sedimentary  strata  that  dip  toward  the  San  Joaquin  Valley  in 
the  monocline  along  the  eastern  flank  of  the  mountains,  and  are 
exposed  on  the  surface  in  a narrow  discontinuous  belt  between  the 
beds  of  Cretaceous  which  underlie  them  and  those  of  the  Miocene 
which  overlie  them.  Broadly  speaking,  the  Tejon  formation  here 
may  be  divided  into  a lower  sandstone  portion  and  an  upper  shale 
portion,  but  no  sharp  division  can  be  made  that  will  be  applicable 
throughout  the  district  under  discussion.  The  most  important  and 
distinctive  feature  of  the  formation  is  the  predominantly  fine-grained 
nature  of  the  beds  toward  the  top  as  compared  with  those  below. 
The  Tejon  comprises  a thickness  of  from  1,400  to  2,300  feet  where 
exposed  most  completely,  the  upper  half  of  which  is  made  up  of  thin 
beds  of  whitish  and  purplish,  siliceous,  argillaceous,  and  locally  cal- 
careous shale  which  is  easily  recognizable  and  which  lends  individu- 
ality to  the  formation.  The  lowermost  few  hundred  feet  are  of 
variable  sandy  beds  locally  fossiliferous.  The  upper  shale  is  very 
similar — especially  in  some  places,  as  north  of  Coalinga — to  the  sili- 
ceous shale  of  the  formation  along  Reef  Ridge  described  later  as  the 
Santa  Margarita,  and  the  two  must  not  be  confused.  Where  the 


24 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Tejon  formation  is  thick,  the  shale  portion  forms  a greater  propor- 
tion of  the  whole  than  does  the  sandstone,  the  middle  beds  beins; 
chiefly  of  fine  grain.  The  middle  beds  differ  from  those  at  the  top 
in  being  more  argillaceous,  of  a darker  color,  less  prominent,  and 
more  frequently  interbedded  with  sandy  beds. 

There  are  three  separate  areas  in  which  the  Tejon  is  exposed,  one 
in  the  oil  field  north  of  Pleasant  Valley,  another  on  the  eastern  border 
of  the  Alcalde  Hills  just  west  of  Coalinga,  and  the  third  along  Reef 
Ridge.  Between  the  Alcalde  Hills  and  Reef  Ridge  it  is  covered,  as 
is  the  Cretaceous  below,  by  the  overlapping  Miocene  beds. 

North  of  Pleasant  Valley. — In  the  northern  region  the  Tejon  is 
typically  exposed  in  the  hills  directly  north  of  Coalinga  in  the  vicinity 
of  the  camp  called  Oil  City.  Here  it  seems  to  be  conformable  with 
the  Chico  and  to  represent  either  continuous  sedimentation  between 
the  Cretaceous  and  Eocene  or  else  a period  of  tranquil  conditions 
between  the  deposition  of  the  two  formations.  The  line  of  contact 
between  them  shown  on  the  map  represents  the  top  of  the  hard, 
brown,  concretionary  beds,  which  are  assumed  to  be  the  uppermost 
Cretaceous  beds  of  this  district.  The  Tejon  (Eocene)  beds  are  mark- 
edly unconformable  with  those  of  Miocene  age  above,  which  lie  with 
a low  dip  upon  the  sharply  folded  and  overturned  shales  character- 
istic of  the  upper  part  of  the  Tejon.  The  formation  is  here  more 
completely  exposed  than  elsewhere  within  the  district  and  has  a thick- 
ness of  at  least  2,300  feet.  The  uppermost  beds  for  a few  hundred 
feet  down  are  chiefly  of  white,  siliceous,  hard  and  brittle,  thinly 
bedded  diatomaceous  and  foraminiferal  shale.  This  shale  grades 
below  into  softer,  crumbly,  very  gypsiferous,  thinly  bedded  clay  shale 
and  sandy  shale  of  a purplish-brown  color,  which  makes  up  the  greater 
part  of  the  formation.  The  shale  is  locally  variable  in  color,  assuming 
different  yellowish  and  reddish  tints  as  the  result  of  staining  by 
petroleum.  It  contains  an  abundance  of  crystallized  gypsum  with 
minor  amounts  of  alkaline  mineral  matter  and  sulphur  along  the 
intricate  fracture  planes.  Numerous  dikes  of  sandstone  traverse  the 
beds  in  various  directions,  and  sand  and  sandstone  of  variable  charac- 
ter are  interbedded  in  lesser  amounts  with  the  shale  in  the  middle  of 
the  formation.  The  lowermost  700  to  1,000  feet  is  made  up  chiefly 
of  interbedded  hard  and  soft  sandstone  that  is  variable  in  color,  but 
is  frequently  yellowish.  The  bedding  throughout  the  formation  is 
usually  thin  and  inconspicuous,  and  especially  in  the  upper  half  is 
apt  to  be  very  irregular. 

Southwest  of  Oil  City  the  Miocene  beds  gradually  lap  more  and 
more  upon  the  Eocene,  leaving  less  of  it  exposed.  Owing  to  lack  of 
exposures  of  the  underlying  rocks  for  1 or  2 miles  north  of  Los  Gatos 
Creek,  where  it  opens  out  to  Pleasant  Valley,  and  the  structural 


GEOLOGY. 


25 


complexity  of  that  area,  the  lines  of  contact  drawn  there  are  theoret- 
ical and  are  at  best  only  approximately  correct. 

South  of  Los  Gatos  Creek. — The  outcrops  of  Tejon  appear  again 
south  of  Los  Gatos  Creek,  in  a belt  along  the  base  of  the  foothills 
facing  Pleasant  Valley.  The  formation  is  conformable  with  the  Chico 
and  the  rocks  near  the  contact  are  fairly  well  exposed.  The  line 
drawn  at  the  top  of  the  concretionary  beds,  which  are  supposed  to 
be  at  the  top  of  the  Chico  (upper  Cretaceous),  marks  the  base  of 
some  beds  of  light-yellow  and  white,  soft,  gypsiferous  sand  that  are 
taken  as  the  lowermost  Tejon  (Eocene)  of  this  district.  Within  100 
feet  above  this  contact  occurs  a bed  of  a calcareous  sandstone  locally 
greatly  hardened  and  full  of  typical  Tejon  fossils.  At  the  two  coal 
mines  northwest  of  Coalinga  the  yellow  sand  at  the  base  of  the  for- 
mation is  exceedingly  gypsiferous  and  variable  in  character,  and 
appears  to  be  a shallow- water  deposit.  It  contains  seams  of  lignite 
and  carbonized  wood,  which  in  former  years  have  been  mined. 
Above  this  sand,  which  has  a thickness  of  about  200  feet,  occur  thin 
beds  of  light-colored,  somewhat  siliceous,  hard  shale,  and  soft,  purplish- 
brown,  gypsum-bearing  argillaceous  shale,  composing  the  upper  half 
of  the  formation.  The  latter  beds  are  steeply  tilted  and  fractured, 
and  their  truncated  edges  are  overlain  by  Miocene  beds  with  low 
dip.  The  unconformity  is  well  exposed  in  the  canyon  of  the  San 
Joaquin  Valley  coal  mine.  At  one  place  4 miles  northwest  of  Coa- 
linga, within  500  to  600  feet  above  the  base  of  the  Tejon,  there  is 
exposed  a bed  of  soft  diatomaceous  shale  which  probably  represents 
part  of  the  siliceous  zone  toward  the  top  of  the  formation  farther 
north,  although  it  is  not  impossible  that  it  occurs  within  the  Miocene 
beds.  Owing  to  the  covering  of  soil  on  the  undulating  ground  at  the 
edge  of  the  plain  northwest  of  Coalinga  the  thickness  and  extent  of 
this  diatomaceous  material,  or  of  the  formation  as  a whole,  can  not 
be  determined.  It  may  be  said,  however,  that  the  shale  portion  of 
the  formation  has  a thickness  in  this  part  of  the  field  of  at  least  300 
feet  below  the  highest  horizon  that  the  unconformably  overlying 
Miocene  leaves  exposed.  The  Miocene  spreads  more  widely  over  the 
Tejon  farther  to  the  south  until  the  strike  of  the  latter  carries  it 
completely  beneath  the  Miocene  beds  at  a point  about  3 miles  west 
of  Coalinga. 

Reef  Ridge. — Beds  of  Tejon  age  appear  again  on  Reef  Ridge,  where 
the  same  broad  lithologic  characteristics  may  be  noted,  namely, 
a sandy,  frequently  yellowish  lower  portion,  and  a purplish  shaly 
upper  portion,  although  many  minor  differences  are  evident  in  the 
manner  of  occurrence  north  and  south  of  the  Miocene  overlap.  The 
Tejon  beds  of  Reef  Ridge,  as  compared  with  those  in  the  northern 
locality,  are  in  general  more  indurated  and  more  regularly  and  steeply 


26 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


tilted.  The  sandstone  is  more  massively  and  regularly  bedded  and 
coarser  at  the  base,  and  the  shale  is  of  different  character  and  .more 
homogeneous.  The  formation  rests  on  what  is  with  little  doubt  a 
lower  portion  of  the  Cretaceous,  probably  unconformably.  An  angu- 
lar unconformity  between  the  Tejon  and  the  Miocene  beds  above  it 
on  Reef  Ridge  was  not  plainly  found  as  it  was  in  the  Coalinga  field, 
but  there  is  good  reason  to  believe  that  an  unconformable  relation 
exists  between  the  two  formations  here  as  well  as  farther  north. 

The  Tejon  of  Reef  Ridge  is  exposed  typically  in  the  gorges  that  cut 
this  ridge  between  Zapato  Canyon  and  Big  Tar  Canyon.  It  is  made 
up  of  a basal  zone  of  conglomerate  ranging  in  thickness  from  a few 
feet  to  over  100  feet,  of  a succession  of  sandstone  beds  aggregating 
about  550  feet  in  thickness,  and  of  an  upper  shale  portion  of  which 
a thickness  as  high  as  900  to  1,000  feet  is  in  places  exposed.  The 
Tejon  becomes  thinner  west  of  Zapato  Canyon  and  is  not  known  to 
outcrop  in  that  direction  west  of  Jasper  Canyon.  Toward  the  south- 
east the  Tejon  passes  under  the  overlapping  Santa  Margarita  (upper 
Miocene)  near  the  extremity  of  Reef  Ridge  and  disappears  entirely. 
Only  one  small  outcrop  of  it  was  found  on  the  southwest  side  of 
McLure  Valley.  It  was  probably  deposited  over  much  of  this 
region  and  later  removed  by  erosion  before  the  deposition  of  the 
Santa  Margarita  formation,  which  rests  directly  upon  the  Cretaceous 
beds.  Rocks  of  Eocene  age  reappear  still  farther  south  in  the  Devils 
Den  region  and  beyond. 

The  sandstone  of  the  Tejon  formation  may  be  easily  recognized  by 
the  prominent  line  of  peaks  that  it  forms  along  Reef  Ridge  a few 
hundred  feet  behind  the  abrupt  frontal  escarpment  produced  by  the 
“Reef  beds.”  It  is  for  the  most  part  homogeneous,  yellowish-gray, 
medium-grained,  oil-stained,  massive  sandstone,  locally  very  hard, 
especially  in  the  upper  portion,  but  usually  fairly  soft.  In  places  it 
is  concretionary  and  becomes  cavernous  by  weathering.  A charac- 
teristic feature  of  it  is  that  it  supports  a heavy  growth  of  vegetation 
as  compared  with  the  shale  above  it.  It  attains  its  greatest  develop- 
ment in  the  central  portion  of  its  extent  and  thins  toward  the  two 
ends  of  Reef  Ridge. 

This  sandstone  contains  typical  Tejon  (Eocene)  invertebrate  fossils 
which  place  it  definitely  in  this  formation  and  allow  its  correlation  with 
the  fossiliferous  sandstone  of  the  Tejon,  already  described  from  the 
Coalinga  field.  At  its  base  it  grades  into  the  locally  variable  conglom- 
erate zone  before  mentioned,  which  is  taken  as  marking  the  base  of 
the  formation  for  the  reason  that  it  rests  unconformably  upon  the 
dark  Cretaceous  shale  in  the  region  of  Big  Tar  Canyon  and  the  head 
of  Garza  Creek.  Farther  west,  however,  in  the  vicinity  of  Canoas 
and  Sulphur  Spring  canyons,  the  coarse  beds  at  this  horizon  rest  with 


GEOLOGY. 


27 


apparent  conformity  and  intergradation  upon  a great  thickness  of 
beds  of  sandstone  and  soft  sandy  shale  and  carbonaceous  clay  shale 
that  are  unlike  Cretaceous  strata  of  other  parts  of  the  district.  It  is 
possible  that  this  underlying  terrane  is  part  of  the  Tejon  formation 
that  is  lacking  elsewhere,  but  it  is  mapped  for  the  present  with  the 
Knoxville-Chico  (Cretaceous).  No  fossils  have  been  found  in  it  and 
sufficient  work  has  not  been  done  upon  it  to  determine  its  relations. 

The  shale  overlying  the  sandstone  of  the  Tejon  is  less  resistant  to 
weathering  and  forms  a belt  of  low  topographic  relief  between  the 
line  of  peaks  formed  by  the  lower  sandstone  and  the  sharp  ridge  of 
the  Vaqueros  (lower  Miocene)  “Reef  beds.”  This  belt  is  marked  by 
few  outcrops  and  is  almost  entirely  bare  of  vegetation  except  grass 
and  scattered  small  juniper  and  oak  trees.  The  rocks  of  this  zone 
are  well  exposed  only  in  the  canyons,  where  they  form  thin  beds  of 
purplish  shale  steeply  tilted  and  considerably  fractured  and  distorted. 
At  the  base  the  beds  of  this  member  are  almost  invariably  poorly 
exposed,  but  they  seem  to  be  somewhat  sandy  through  a thickness 
of  about  200  feet,  as  if  representing  a transition  from  the  sandstone 
of  the  lower  member.  Above  this  transition  zone  the  beds  are  fine- 
grained argillaceous  and  siliceous  shale,  usually  finely  comminuted, 
of  a peculiar  dark  purplish-brown  color,  and  similar  to  some  of  the 
shale  in  the  upper  member  of  the  formation  north  of  Coalinga. 
Many  of  the  cracks  in  the  shale  are  lined  with  sulphur.  Toward  the 
top  the  shale  becomes  in  places,  as  near  and  southeast  of  Big  Tar 
Canyon,  of  a yellowish  or  whitish  color,  and  both  siliceous  and  calca- 
reous, the  latter  variety  containing  innumerable  foraminiferal  remains. 
These  varieties  bring  out  still  more  strikingly  the  resemblance  to  the 
shale  member  north  of  Coalinga  and  leave  little  doubt  that  the  same 
horizon  is  represented  in  both  localities.  The  thickness  of  beds 
exposed  between  the  sandstone  member  of  the  Tejon  and  the  Miocene 
varies  from  place  to  place  along  Reef  Ridge.  The  maximum  thick- 
ness that  has  been  found  is  in  the  neighborhood  of  Canoas  Creek, 
where  it  is  about  1,000  feet. 

Age  and  relations  of  the  shale  of  the  Tejon  formation. — No  very 
characteristic  fossils  have  been  found,  either  in  the  northern  or  in  the 
southern  parts  of  the  district,  in  the  shale  overlying  the  sandstone 
known  to  belong  to  the  Tejon  formation,  and  therefore  its  classifica- 
tion with  the  Tejon  is  not  final.  It  is  considered  as  a portion  of  the 
Tejon  (Eocene)  because  it  is  in  apparent  continuity  with  the  beds  of 
that  age,  because  it  is  found  in  association  with  those  beds  wherever 
they  occur,  because  it  underlies  unconformably  beds  containing 
fossils  of  lowest  Miocene  age,  and  because  it  contains  fossils  that 
point  to  its  Eocene  age.  It  is  not  thought  probable  that  it  belongs 
in  the  Oligocene,  because  rocks  of  that  age  have  not  been  recognized 


28 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


in  the  Coast  Range  south  of  the  Santa  Cruz  Mountains.  The  uncon- 
formity between  this  shale  and  the  lower  Miocene  is  profound  in  the 
Coalinga  field.  On  Reef  Ridge  it  is  not  apparent  along  the  contact, 
but  the  tilting  of  the  shale  beds  is  in  general  steeper  and  the  dis- 
turbance greater  than  in  the  Miocene  above.  At  the  northwest  end 
of  Reef  Ridge  the  Yaqueros  (lower  Miocene)  overlaps  and  rests 
directly  upon  the  dark  shale  of  the  lower  portion  of  the  Knoxville- 
Chico,  proving  for  this  portion  of  the  district,  as  well  as  the  northern 
portion,  the  existence  of  an  important  unconformity  between  the 
Tejon  and  the  Vaqueros.  The  variable  thickness  of  the  shale  of  the 
Tejon  formation  exposed  along  Reef  Ridge  indicates  an  overlapping 
of  the  Miocene  upon  different  horizons,  and  the  fact  that  the  light- 
colored  calcareous  and  siliceous  shales  that  are  characteristic  of  the  * 
uppermost  horizon  in  the  Coalinga  field  are  absent  in  most  places 
along  Reef  Ridge,  though  present  in  others,  is  a further  proof  of  the 
existence  of  such  overlaps. 

Importance  with  relation  to  petroleum. — The  shale  in  the  upper  part 
of  the  Tejon  is  thought  to  be  the  source  of  the  petroleum  found  in  the 
Coalinga  district.  The  sandstone  both  above  and  below  it  is  saturated 
and  stained  with  oil,  and  although  the  shale  itself  does  not  give 
evidence  of  containing  much  petroleum  it  shows  the  effects  of  being 
stained  by  it.  Petroleum  has  not  been  found  in  this  district  except 
in  beds  associated  with  the  Tejon,  and  where  the  Tejon  is  absent  the 
beds  of  the  other  formations  are  dry.  Along  Reef  Ridge  the  sand- 
stone of  the  lower  half  of  the  formation  is  saturated  with  oil,  in  places 
through  its  whole  thickness.  The  sand  has  a strong  odor  and  when 
a fresh  fracture  surface  is  exposed  it  is  found  to  be  stained  brown 
throughout.  Included  layers  of  shale  are  stained  purple.  All  the 
wells  that  are  drilled  through  the  shale  to  this  sandstone  strike  oil 
in  it  in  small  amounts.  The  great  thickness  of  the  sandstone  through 
which  the  oil  has  permeated  lessens  the  probability  of  its  being  found 
in  large  amounts  locally.  It  is  probable  that  this  oil  originated  in 
the  shale  above  and  became  absorbed  in  the  sandstones  above  and 
below.  The  occurrence  of  oil  in  the  overlying  Miocene  beds  will  be 
mentioned  later. 

It  is  believed  that  the  shale  in  the  upper  part  of  the  Tejon  contains 
a large  proportion  of  material  of  organic  origin.  The  calcareous 
facies  is  composed  in  part  of  foraminiferal  remains,  and  the  hard 
siliceous  beds  are  very  similar  to  the  altered  varieties  of  diatomaceous 
and  foraminiferal  shale  found  in  other  formations  in  other  parts  of  the 
State.  In  places  in  this  district  the  shale  is  softer  and  less  altered 
and  is  composed  largely  of  diatom  remains.  It  is  probable  that  these 
small  marine  organisms  have  been  the  chief  source  of  the  oil. 

In  other  parts  of  California  the  origin  of  the  petroleum  is  ascribed 
to  formations  of  similar  peculiar  character,  although  of  different  age, 


GEOLOGY. 


29 


and  it  is  a striking  fact  that  all  the  conditions  point  to  the  diatoma- 
ceous  or  foraminiferal  nature  of  the  deposits  as  the  determining  factor 
in  the  original  occurrence  of  petroleum  rather  than  to  the  age  or 
other  characteristics  of  the  formations. 

THE  POST-EOCENE  FORMATIONS. 

General  statement. — The  Miocene,  Pliocene,  and  early  Pleistocene 
periods  are  represented  in  the  Coalinga  district  by  a series  of  forma- 
tions that  form  a group  by  themselves,  distinct  from  the  older 
formations.  The  first  impression  received  on  viewing  the  field  is 
that  the  later  Tertiary  beds  form  one  continuous  succession,  and  it 
mis  therefore  natural  to  take  up  first  a brief  review  of  the  whole  series 
-before  passing  to  the  more  detailed  description  of  the  different  divi- 
sions of  it,  which  on  closer  study  are  found  to  be  separable  from  one 
another. 

The  Miocene  epoch  was  occupied  in  the  Coalinga  district  by  fairly 
continuous  marine  conditions.  There  was  rapid  erosion  of  areas  of 
considerable  relief  situated  probably  along  the  line  of  the  present 
mountainous  belt,  and  deposition  of  the  eroded  material  in  great 
thicknesses  in  changing  and,  for  the  most  part,  slowly  subsiding  sub- 
merged basins.  The  formations  thus  deposited  underwent  disturb- 
ances during  these  periods,  and  were  finally  affected  as  a whole  after 
the  close  of  the  Tertiary  by  the  land  movements,  to  which  the  greater 
part  of  the  disturbance  at  present  visible  in  the  beds  is  due.  As  a 
result  of  these  processes  the  periods  following  the  Eocene  are  here 
represented  by  a great  series  of  sandstone  and  shale  and  conglomer- 
ate beds,  all  tilted  at  about  the  same  angle,  having  usually  similar 
characteristics  and  presenting  an  almost  perfect  appearance  of  con- 
formity and  intergradation.  By  means,  however,  of  discontinuous 
fossil  faunas,  distinguishable  lithologic  groups,  the  absence  in  some 
places,  as  a result  of  overlap,  of  formations  or  zones  known  elsewhere, 
and  the  appearance  of  fragments  of  older  formations  within  younger 
ones,  several  important  breaks,  which  prove  the  intervention  of 
periods  of  time  during  which  land  conditions  existed  over  wide  areas 
or  locally,  may  be  definitely  made  out.  The  important  post-Eocene 
formations  that  represent  the  epochs  of  submergence  of  the  land  in  the 
area  now  occupied  by  the  Coalinga  district  are  the  Vaqueros  (lower 
Miocene),  the  Santa  Margarita  (upper  middle  Miocene),  the  Jacalitos 
(early  upper  Miocene),  and  the  Etchegoin  (late  upper  Miocene). 
The  formation  following  these,  the  Paso  Robles  (Pliocene  and  lower 
Pleistocene),  is  probably  in  large  part  of  different  origin,  but  is  simi- 
lar to  the  others  in  the  general  features  of  its  appearance.  These 
formations  are  all  united  into  one  series  in  the  monocline  dipping 
down  the  east  flank  of  Joaquin  Ridge  in  the  northern  part  of  the 
district  and  again  in  the  monocline  dipping  away  from  Reef  Ridge 


30 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


in  the  southern  portion,  but  the  character  of  the  series  is  not  entirely 
the  same  in  the  two  regions. 

The  series  in  the  north. — In  the  northern  part  of  the  district  the 
base  of  the  Miocene-Pliocene  is  formed  of  coarse  and  fine  oil-impreg- 
nated sands  unconformably  overlying  the  whitish  and  purplish 
petroliferous  Eocene  (Tejon)  shales,  these  sands  being  overlain  by 
prominent  sandstone  beds,  by  a prominent  zone  of  white  siliceous 
shale,  and  by  soft  sand,  up  to  the  base  of  a zone  of  bluish  and  varie- 
gated clay  and  sand  locally  known  as  the  “Big  Blue.”  Up  to  this 
point  the  beds  are  fossiliferous,  have  a thickness  of  about  550  feet, 
and  are  mapped  as  Vaqueros  (lower  Miocene).  The  “Big  Blue”  has 
a thickness  of  about  300  feet  and  is  unfossiliferous.  It  is  overlain 
by  a' thickness  of  about  175  feet  of  coarse  sand  and  sandstone  beds 
full  of  immense  oysters,  barnacles  {Tamiosoma) , scallop  shells  ( Pec- 
ten) , and  other  fossils,  which  beds  may  be  named  the  Tamiosoma 
zone.  This  is  overlain  by  400  to  500  feet  of  sand  and  gravel  beds  up 
to  the  base  of  a very  prominent  gravel  zone  .full  of  petrified  wood. 
The  beds  from  the  base  of  the  “Big  Blue ” up  to  this  point  are  mapped 
as  the  Santa  Margarita  (upper  middle  Miocene)  formation.  The 
fossil-wood  and  gravel  zone  forms  the  base  of  a succession  of  sand, 
sandstone,  gravel,  and  clay  beds  extending  up  to  the  base  of  a prom- 
inent zone  of  bluish-gray  sand  beds,  having  near  their  base  a rich 
fossil  bed  (the  Glycymeris  zone).  The  succession  of  beds  up  from 
the  base  of  the  gravel  zone  to  this  point  has  a thickness  of  about 
1,600  feet,  and  is  mapped  as  the  Jacalitos  formation  (early  upper 
Miocene).  The  fossil  bed  and  bluish  sands  immediately  overlying 
grade  upward  into  sand  and  clay  beds,  the  whole  forming  a thick- 
ness of  about  1,700  feet,  which  is  mapped  as  the  Etchegoin  formation 
(uppermost  Miocene),  and  this  finally  is  overlain  by  poorly  exposed 
coarse  gravel  deposits,  which  are  mapped  as  the  Paso  Robles  forma- 
tion (Pliocene-lower  Pleistocene).  The  total  thickness  of  the  suc- 
cession in  the  Coalinga  field  thus  outlined  is  about  4,600  feet,  exclu- 
sive of  the  Paso  Robles  formation,  which  can  not  be  measured  in 
this  portion  of  the  district. 

The  series  in  the  south. — In  the  southern  part  of  the  district  the 
basal  portion  of  the  Miocene-Pliocene  consists  of  about  700^  to  900 
feet  of  steeply  dipping  hard  sandstone  and  conglomerate  beds,  form- 
ing the  face  of  Reef  Ridge.  These  overlie  with  an  important,  though 
usually  not  apparent,  unconformity  the  shale  of  the  Tejon  (Eocene), 
and  arc  locally  petroliferous.  At  the  summit  they  grade  into  softer 
beds  overlain  by  hard  siliceous  shale.  Up  to  this  shale  the  beds  are 
fossiliferous,  and  are  mapped  as  the  Vaqueros  sandstone.  The  over- 
lying  shales  are  hard  and  whitish,  form  a prominent  zone  varying  up 
to  1,200  feet  in  thickness,  and  are  mapped  as  Santa  Margarita, 
although  only  tentatively  referred  to  that  formation.  These  shales 


GEOLOGY. 


31 


are  overlain  by  a great  succession  of  beds  of  sandstone,  shale,  sand, 
clay,  gravel,  and  conglomerate  of  many  varieties,  having  a thickness, 
as  measured  in  a section  south  of  Big  Tar  Canyon,  of  at  least  9,500 
feet,  and  presenting  no  prominent  line  of  constant  variation  which 
may  be  taken  as  a separation  between  distinct  terranes.  This  suc- 
cession is,  however,  divided  on  the  map,  on  the  basis  of  criteria  to  be 
discussed  later  (pp.  40-61),  into  three  approximately  equal  divisions 
corresponding  to  the  formations  in  the  north,  namely,  the  Jacalitos 
(early  upper  Miocene),  Etchegoin  (uppermost  Miocene),  and  the  Paso 
Robles  (Pliocene-lower  Pleistocene).  The  total  thickness  of  the 
Miocene-Pliocene  and  the  lower  Pleistocene  measurable  in  the  above- 
mentioned  single  section  is  over  11,000  feet. 

VAQUEROS  SANDSTONE  (LOWER  MIOCENE). 

General  description.— The  unconformity  at  the  top  of  the  Tejon 
(Eocene)  marks  an  important  lapse  of  time  before  the  beginning  of 
the  Miocene  epoch.  In  the  early  Miocene  a sedimentary  formation 
was  deposited  in  the  Coalinga  district  that  is  the  correlative  of  the 
formation  known  as  the  Yaqueros  sandstone  in  the  region  nearer  the 
coast.  The  contemporaneity  of  these  formations  is  shown  by  the 
fact  that  the  fossil  remains  of  mollusks  characteristic  of  lower  Miocene 
time  exist  in  both. 

The  Vaqueros  sandstone  in  the  area  under  discussion  forms  an 
elongated  belt  east  of  the  belt  of  Tejon  in  the  hills  bordering  the 
San  Joaquin  Valley.  It  consists  of  hard  and  soft  sandstone,  shale, 
and  conglomerate,  varying  from  550  feet  in  the  Coalinga  field  to  900 
feet  in  the  Kreyenhagen  field,  and  may  be  easily  distinguished  from 
all  other  formations  by  the  protruding  tendency  of  the  hard  sand- 
stone, known  as  the  “Reef  beds,”  in  its  central  portion.  These  beds 
outcrop  prominently  in  the  northern  portion  of  the  district,  and  again 
in  the  southern  portion  assume  such  prominence  as  to  dominate  the 
landscape  on  the  bold  face  of  Reef  Ridge.  They  are  much  more 
resistant  to  erosion  than  the  soft  associated  beds,  and,  dipping  toward 
the  valley  on  the  northeast  at  an  angle  varying  from  50°  to  80°,  they 
form  the  scarp  and  double  row  of  pinnacles  of  Reef  Ridge  fronting 
the  foothills  on  that  side. 

An  important  distinguishing  feature  of  the  Vaqueros  is  that  the 
beds  at  its  base  are  the  chief  oil  sands  of  the  Coalinga  district.  In 
many  places  they  are  saturated  and  discolored  with  petroleum. 
They  rest  upon  the  eroded  surface  of  the  shale  of  the  Tejon  through- 
out most  of  their  extent,  but  overlap  in  the  Alcalde  and  Jacalitos 
hills  upon  the  Knoxville-Chico  (Cretaceous)  rocks,  thus  hiding  the 
Tejon  (Eocene)  from  view.  Where  such  overlapping  occurs,  the 
basal  beds  lose  their  petroliferous  character  at  a distance  from  the 
Tejon. 


32 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


There  are  three  different  areas  along  the  belt  of  outcropping 
Vaqueros  which  deserve  separate  description  owing  to  the  diversity 
of  character  assumed  by  the  formation  in  them.  One  of  these  is 
in  the  oil  field  north  of  Coalinga,  a second  extends  from  a point  in 
the  Alcalde  Hills  west  of  Coalinga  to  Waltham  Creek,  and  the  third 
extends  along  Reef  Ridge.  The  first  two  areas  are  separate.  The 
second  and  third  areas  are  shown  on  the  map  as  discontinuous,  but 
it  is  possible  that  a narrow  belt  of  Vaqueros  is  exposed  south  of 
Waltham  Creek,  and  that  this  connects  with  the  belt  on  Reef  Ridge. 

North  of  Pleasant  Valley. — In  the  hills  north  of  Coalinga  the  forma- 
tion includes  all  the  beds  overlying  the  Tejon  at  least  as  far  up  in  the 
series  as  the  base  of  the  zone  of  fine  grayish  sand  and  clay  locally 
well  known  as  the  “Big  Blue,”  and  possibly  to  the  summit  of  this 
zone,  which  is  at  the  base  of  the  Tamiosoma  zone.  The  “Big  Blue” 
is  not  known  to  be  fossiliferous  and  presents  therefore  no  definite 
basis  for  correlating  it,  but  it  is  mapped  for  the  present  as  a portion 
of  the  overlying  formation  (the  Santa  Margarita)  and  the  summit  of 
the  Vaqueros  is  placed  at  its  base.  The  Vaqueros  formation  is 
thereby  restricted  to  those  beds  which  are  known  by  their  fossils  to 
belong  to  it.  Its  thickness  is  about  550  feet. 

The  lowest  bed  of  the  formation  is  coarse,  irregular,  pebbly  sand 
truncating  the  eroded  edges  of  the  Tejon  formation.  It  is  followed 
above  by  rough-bedded,  hard  and  soft,  both  coarse  and  fine  sand- 
stone, sandy  shale,  and  pure  shale.  These  basal  beds  for  100  or  200 
feet  up  are  thoroughly  impregnated  with  oil  and  have  a dark-brown 
color  due  to  staining,  a strong  odor,  and  a curious  mode  of  fracturing 
characteristic  of  rock  that  is  filled  with  bitumen.  About  225  feet 
above  the  base  is  a hard  zone  ranging  from  5 to  15  feet  in  thickness, 
made  up  of  several  calcareous  sandstone  layers  and  a rough  mixture 
of  ingredients  of  different  kinds  and  textures.  This  zone  of  hard 
sandstone  forms  a prominent  outcrop  over  the  summit  and  down  the 
sides  of  a hill  just  east  of  the  road  leading  up  Oil  Canyon,  appearing 
from  a distance  like  a portion  of  the  periphery  of  a huge  wheel. 
Owing  to  the  tendency  of  this  bed  to  jut  out  over  the  surface  of  the 
hills,  it  was  referred  to  as  the  “Reef  beds”  by  F.  M.  Anderson,®  and 
the  name  is  here  retained  for  convenience  of  reference. 

Similar  hard  and  soft  sandstone  beds  continue  to  about  425  feet 
above  the  base  of  the  formation,  where  a bed.  10  to  20  feet  thick  of 
compact,  white,  diatomaceous  and  foraminiferal  shale  is  sharply 
interbedded.  This  bed  is  prominent  and  so  sharply  marked  off  from 
the  associated  gray  sand  that  it  can  be  easily  traced.  It  has 
been  referred  to  throughout  the  field  work  as  the  “Indicator,”  and 
the  name  was  found  so  convenient  that  it  has  been  retained  in 


a A stratigraphic  study  in  the  Mount  Diablo  Range  of  California:  Proc.  California  Acad.,  Sci.,  3d 
ser.,  Geology,  vol.  2,  No.  2,  1905,  p.  175. 


GEOLOGY. 


33 


this  report.  The  bed  is  continuous  and  in  the  same  relative  position 
everywhere,  from  Oil  Canyon  to  the  northern  edge  of  the  area  shown 
on  the  map,  beyond  which  no  attempt  was  made  to  trace  it.  South- 
west of  Oil  Canyon  it  is  continuous  for  a mile  or  two  at  least.  It 
preserves  its  strong  individuality  throughout  in  spite  of  the  fact  that 
it  changes  in  character  locally  from  a soft,  compact,  earthy  deposit, 
both  massively  bedded  and  finely  laminated  (as  on  the  eastern  side 
of  Oil  Canyon  in  the  south-central  part  of  sec.  20)  to  a hard,  thinly 
bedded,  white,  porcelaneous  or  flinty  shale  and  yellowish  calcareous 
shale  (as  south  of  the  Laval  grade  on  the  hill  (elevation  2,024  feet) 
8J  miles  north  of  Cqalinga  in  the  western  half  of  sec.  21).  This  bed, 
where  not  greatly  indurated,  may  be  seen  with  a lens  to  be  full  of 
diatom  remains — in  fact,  the  rock  seems  to  be  chiefly  composed  of 
them.  It  is  strikingly  similar  to  the  siliceous  shale  characteristic 
of  the  upper  part  of  the  Tejon  (p.  23),  and  of  the  Santa  Margarita 
formation  of  Reef  Ridge  (p.  37). 

Above  the  “ Indicator’ 1 bed  soft  gray  and  brown  sandstones  in 
thin  layers  make  up  a variable  zone  about  125  feet  thick.  This 
sandstone  contains  typical  Yaqueros  (lower  Miocene)  fossils,  and  is 
the  uppermost  horizon  at  which  they  are  found.  It  grades  above 
into  soft,  fine,  grayish- white  sand  that  looks  bluish  from  a distance — 
the  well-known  “Big  Blue.”  The  latter  zone  being  unfossiliferous, 
the  line  for  the  top  of  the  Yaqueros  formation  is  drawn  at  its  base. 

Southwest  of  Oil  Canyon  the  Yaqueros  beds  become  much  thinner, 
and  within  about  2 miles  they  lose  their  prominence.  In  the  hills 
for  2 miles  north  of  the  head  of  Pleasant  Y alley  the  beds  are  largely 
hidden  by  recent  deposits  of  soil,  alluvium,  and  gravel,  but  it  is 
probable  that  a small  thickness  of  beds,  representing  a part  of  the 
Vaqueros,  is  continuous.  Their  presence  is  doubtfully  indicated  by 
certain  fossils  that  have  been  found. 

Alcalde  Hills. — In  the  hills  west  of  Coalinga  the  Yaqueros  is  absent 
north  of  the  San  Joaquin  coal  mine,  with  the  possible  exception  of  a 
thin  discontinuous  zone  locally  exposed  beneath  the  Santa  Margarita 
and  Jacalitos  formations.  South  of  the  coal  mine  incoherent  and 
extremely  fossiliferous  beds  of  the  Yaqueros  formation,  largely  of 
yellowish  and  gray  sand,  overlap  upon  the  Tejon  and  Chico  (Upper 
Cretaceous).  Here,  as  in  the  Eastside  field,  they  are  about  500  feet 
thick.  The  sand  is  both  coarse  and  fine,  roughly  bedded,  and  has 
partings  and  lenses  of  hard  sandstone  and  gravel.  Although  it  is 
fossiliferous,  the  fossils  are  poor  and  not  certain  as  indicators.  A 
section  of  the  Yaqueros  and  overlying  formations  from  Anticline 
Canyon  to  the  Lucile  oil  well  is  given  under  the  discussion  of  the 
developed  territory  (p.  101).  Farther  west  a capping  of  low-dipping 
beds  of  this  age  extends  over  the  ridges  formed  of  steeply  dipping 
beds  of  the  Knoxville-Chico.  This  capping  is,  for  the  most  part, 
52332— Bull.  357—08 3 


34 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


only  slightly  indurated  sand,  clay,  and  gravel  of  many  varieties  of 
color  and  texture. 

Jacalitos  Hills. — Between  Waltham  Creek  and  the  northern  end 
of  Reef  Ridge  the  Yaqueros  has  not  been  recognized,  but  it  may 
form  a belt  around  the  southeastern  side  of  Curry  Mountain,  through 
the  area  tentatively  mapped  as  covered  by  the  Jacalitos  formation, 
and  thence  continue  southward,  beyond  the  limits  mapped,  to  join 
the  belt  on  Reef  Ridge. 

Reef  Ridge. — The  Yaqueros  overlies  the  shale  of  the  Tejon  on  Reef 
Ridge  and  forms  the  steep  face  of  the  ridge.  Southward  from  the 
region  around  Pleasant  Yalley  the  deposits  thicken,  and,  owing  to 
greater  induration,  form  a more  conspicuous  part  of  the  landscape 
than  the  contemporary  beds  farther  north.  Their  relation  to  the 
underlying  shale  of  the  Tejon  is  probably  unconformable,  although 
no  wide  disparity  in  dip  has  been  observed.  There  is  even  an  appar- 
ent gradation  from  the  shale  below  to  the  sandstone  above  in  some 
places,  making  it  difficult  to  determine  the  exact  contact  between 
the  two  formations.  This  difficulty  is  largely  due  to  the  lack  of  con- 
tinuous exposures  near  the  contact. 

The  Yaqueros  is  subject  to  considerable  variation  from  place  to 
place,  as  will  be  shown  in  the  tabulated  sections  on  page  35.  It 
may  in  general  be  divided  into  three  parts,  one  of  comparatively  soft 
beds  of  sandstone  with  shaly  sandstone  at  the  base,  comprising  about 
one-fourth  of  the  total  thickness;  a second  of  hard,  fossiliferous  beds 
of  sandstone  with  some  conglomerate,  making  up  about  half  of  the 
formation  and  producing  the  prominent  outcrops  of  Reef  Ridge;  and 
a third  similar  in  thickness  and  character  to  the  first  and  grading  into 
soft,  fine-grained  beds  that  are  poorly  exposed  and  lead  the  observer 
to  think  there  is  a transition  to  the  shale  of  the  Santa  Margarita  for- 
mation above,  although  this  is  hardly  supposable.  The* third  part  is 
much  thicker  on  Canoas  Creek  than  elsewhere,  and  there  makes  up  half 
of  the  formation.  The  Vaqueros  sandstone  is  thicker  in  the  southeast- 
ern than  in  the  northwestern  half  of  Reef  Ridge,  the  thickest  section 
observed  being  900  feet,  on  Canoas  Creek.  The  middle  part  is  marked 
by  three  principal  horizons  of  hard  fossiliferous  sandstone  and  con- 
glomerate beds,  that  stand  out  in  strong  relief.  The  lowest  and 
middle  beds  are  about  150  to  200  feet  apart  and  the  middle  and  upper- 
most beds  100  feet  apart  on  the  average.  They  vary  in  relative 
prominence  from  place  to  place  and  the  exact  horizon  at  which  the 
induration  is  most  pronounced  is  variable. 


GEOLOGY. 


35 


The  following  sections  give  an  idea  of  the  character  of  the  Yaqueros 
as  it  occurs  typically  exposed  along  Reef  Ridge: 


Section  of  Vaqueros  formation  in  Canoas  Canyon. 


Feet. 


Soft  fine  sandstone  with  large  oil  seepages;  “Button  beds”  at  base  containing 
Astrodapsis,  etc.;  overlain  by  siliceous  shales  of  the  Santa  Margarita  forma- 
tion  180 

Hard  and  soft,  gray  and  brown-stained  sandstone,  with  large  oil  seepages  in 

upper  half 300 

Massive  sandstone  beds  with  thick,  very  prominent  hard  beds  at  top  and  at 

base,  the  “Reef  beds;”  fossils  at  base 100 

Sandstone  with  very  prominent  hard  bed  at  base 200 

Fairly  hard,  thin-bedded  sandstone  underlain  by  the  Tejon  formation 120 


900 

Section  of  Vaqueros  in  Big  Tar  Canyon. 

Feet. 


Soft  sandstone  and  sandy  shale,  apparently  a transition  zone  from  Yaqueros  to 

Santa  Margarita 200 

Two  extremely  hard  fossiliferous  sandstone  and  conglomerate  beds,  each  about 
10  feet  thick  (“  Reef  beds,  ’ ’ with  less  prominent,  softer  sandstone  between) ...  75 

Coarse  sandstone 150 

Thinibedded  hard  sandstone  and  shale,  with  reddish-brown  shale  at  base 100 

Massive,  fairly  soft  grayish-brown  sandstone 50 

Soft  sandstone  with  oil-stained  streaks  all  through,  overlying  purple  shale  of 

Tejon;  spring  of  tarry  oil  at  base 200 


Importance  with  relation  to  petroleum. — The  Yaqueros  sandstone 
constitutes  the  principal  reservoir  for  the  petroleum  in  the  Coalinga 
district.  The  oil  enters  the  formation  from  the  underlying  Tejon 
and  collects  most  abundantly  in  certain  favorable  zones  within  the 
formation,  chiefly  at  its  base,  although  permeating  locally  the  whole 
formation  in  lesser  amounts.  The  summit  of  the  formation,  as 
mapped,  being  overlain  by  the  “Big  Blue”  north  of  Coalinga,  it  is 
coincident  with  the  top  of  the  productive  zone  in  the  Eastside  field. 
Similarly  it  is  believed  that  the  productive  zone  in  the  Kreyenhagen 
field  does  not  reach  higher  than  the  Yaqueros,  the  formation  being 
there  overlain  by  the  impervious  shales  of  the  Santa  Margarita.  The 
relation  of  the  formation  to  the  occurrence  of  the  petroleum  is  dis- 
cussed more  fully  elsewhere.  (See  p.  69.) 

SANTA  MARGARITA  FORMATION  (UPPER  MIDDLE  MIOCENE). 


General  description. — A zone  of  beds  full  of  very  large  fossil  oysters 
and  barnacles  runs  through  the  midst  of  the  developed  oil  territory  in 
the  Eastside  field  and  is  well  known  to  those  familiar  with  the  field. 
Its  fossils  show  that  it  belongs  in  the  same  portion  of  the  geologic 
column  as  the  Santa  Margarita  formation®  in  San  Luis  Obispo 


Fairbanks,  H.  W.,  Geologic  Atlas  U.  S.,  San  Luis  folio  (No.  101),  U.  S.  Geol.  Survey,  1904. 


86 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


County,  farther  toward  the  coast.  This  formation  belongs  in  the 
upper  part  of  the  middle  Miocene.  No  fossils  have  been  found  in  the 
beds  immediately  below  or  above  the  Tamiosoma  zone,  as  the  fossil 
beds  referred  to  may  be  termed,  from  the  typical  and  restricted 
occurrence  in  them  of  the  large  barnacle  of  that  genus,  but  the  beds 
below  and  above,  for  a thickness  of  several  hundred  feet,  are  for  the 
present  mapped  in  the  same  formation  with  the  fossil  beds  because 
they  are  closely  associated  with  them  and  to  all  appearances  form  a 
part  of  the  same  succession.  The  Santa  Margarita  formation  is 
traceable  only  as  far  south  as  the  San  Joaquin  coal  mine.  Beyond 
that  the  beds  are  either  lacking  or  are  unfossiliferous,  so  that  it  can 
not  positively  be  stated  that  they  are  the  same.  In  a region  such  as 
this,  where  the  beds  are  so  variable  from  place  to  place  and  the  dif- 
ferent formations  so  similar,  the  fossils  furnish  the  only  evidence  of 
contemporaneity  that  holds  good.  In  the  Kreyenhagen  field,  there- 
fore, where  the  portion  of  the  series  between  the  Yaqueros  (lower 
Miocene)  and  Jacalitos  (upper  Miocene),  corresponding  to  the  portion 
occupied  by  the  Santa  Margarita  farther  north,  is  made  up  of  unfos- 
siliferous; hard,  largely  white,  siliceous  shales,  it  can  not  be  stated 
definitely  whether  or  not  a continuation  of  the  Santa  Margarita  occurs. 
The  break  in  the  geologic  column  between  the  Yaqueros  (lower  Mio- 
cene) and  Jacalitos  (upper  Miocene)  is  great,  covering  the  whole 
of  middle  Miocene  time,  and  is  represented  only  in  its  later  part  by  the 
Tamiosoma  zone  and  associated  beds.  The  Monterey  formation 
(early  middle  Miocene)  of  the  region  nearer  the  coast  is  lacking.  It 
is  possible  that  the  beds  overlying  the  Yaqueros  formation  in  the 
two  parts  of  the  Coalinga  district  represent  different  divisions  of  the 
later  part  of  the  middle  Miocene  period,  that  in  the  Kreyenhagen 
Hills  being  perhaps  later.  The  rocks  in  the  two  fields  are  for  the 
present  mapped  as  one  formation,  the  Santa  Margarita. 

Coalinga  field. — The  basal  part  of  the  formation  mapped  as  the 
Santa  Margarita  is  the  k‘Big  Blue.”  This  consists  usually  of  about 
300  feet  of  light-gray  fine  sand  and  clay  that  appears  to  have  a light- 
bluish  tinge,  especially  when  moistened;  locally  it  includes  other 
materials,  causing  it  to  be  one  of  the  most  varied  zones  in  the  region. 
It  is  recognized  in  the  oil  wells  as  a sticky  and  frequently  tough  sand 
and  clay  immediately  overlying  the  oil  sands.  Toward  the  northern 
edge  of  the  area  mapped  it  becomes  coarser  and  is  made  up  largely  of 
fine-grained,  coarse-grained,  and  bowlder  beds  composed  of  serpentine 
fragments,  evidently  derived  from  an  area  of  serpentine  to  which  the 
basin  of  deposition  was  in  close  proximity.  Some  of  these  serpentin- 
ous  beds  are  extremely  hard  and  form  prominent  buttes  in  which  the 
decaying  serpentine  presents  a variety  of  shades  of  light  blue,  green, 
brown,  and  dark  red. 


GEOLOGY. 


37 


The  “Big  Blue”  is  overlain  by  the  Tamiosoma  zone  which  com- 
prises a thickness  of  about  175  feet  of  fossiliferous,  fine,  medium- 
orained  and  locally  gray  sand  and  some  sandy  clay.  This  in  turn  is 
overlain  by  400  to  500  feet  of  alternating  beds  of  fine  sand,  sandy 
clay,  coarser  sand,  and  gravel  up  to  the  base  of  the  prominent  and 
thick  gravel  zone  considered  as  marking  the  base  of  the  Jacalitos. 

Toward  the  southwest  the  Santa  Margarita  formation  disappears 
east  of  Oil  Canyon,  being  overlapped  by  the  Jacalitos.  It  is  not 
known  just  where  the  overlap  occurs,  because  the  beds  are  poorly 
exposed  and  cease  to  have  distinguishing  characters.  On  the  western 
side  of  Pleasant  Valley  the  Tamiosoma  zone  reappears  and  overlaps 
directly  upon  the  Tejon  (Eocene)  at  the  San  Joaquin  coal  mine. 
This  is  the  southernmost  point  at  which  the  fossils  of  this  zone  have 
been  found  within  the  district,  and  south  of  there  the  Tamiosoma 
zone  is  either  absent  or  overlapped  by  the  Jacalitos  formation.  There 
is  present,  however,  beneath  the  fossiliferous  Jacalitos  beds,  between 
the  coal  mine  and  Waltham  Creek,  a zone  of  bluish  and  grayish  clay, 
about  250  feet  thick,  mapped  with  the  Vaqueros  of  that  area,  that 
may  possibly  represent  the  same  horizon  as  the  “Big  Blue”  in  the 
Eastside  field.  If  this  be  true,  it  indicates  a closer  relationship  of  the 
“Big  Blue”  to  the  underlying  Vaqueros  than  to  the  Santa  Margarita, 
with  which  this  zone  has  been  described.  This  zone  is  described  in 
the  geologic  section  from  Anticline  Canyon  to  the  Lucile  oil  well, 
page  101. 

Kreyenhagen field. — The  Vaqueros  sandstone  all  along  Reef  Ridge 
is  overlain  by  a formation  of  purplish,  white,  and  brownish  siliceous 
and  argillaceous  shale,  having  a thickness  varying  between  50  and 
1,200  feet.  The  thin  sharp  beds  of  shale  dip  steeply  away  from  Reef 
Ridge  to  the  northeast,  their  upturned  edges  being  exposed  in  a belt, 
usually  only  a few  hundred  feet  wide,  that  follows  the  face  of  the 
ridge.  This  belt  is  likewise  a topographic  feature,  owing  to  the  resist- 
ance of  the  beds,  which  produce  a line  of  shoulders  or  knobs  on  the 
small  lateral  ridges  descending  toward  the  foothills.  Southeast  of 
Little  Tar  Canyon  the  ridge  of  the  Pyramid  Hills,  composed  entirely 
of  the  shale,  is  a still  more  marked  expression  of  this  topographic 
influence,  which  is  likewise  characteristic  of  the  formation  elsewhere. 
The  features  described  make  this  shale  easily  recognizable  as  a litho- 
logic unit  with  strong  individuality,  and  distinguish  its  main  portion 
markedly  from  the  Vaqueros  sandstone  (lower  Miocene)  below  and 
the  soft  sandstone  beds  of  the  Jacalitos  (upper  Miocene)  above.  As 
before  stated,  this  shale  is  only  tentatively  referred  to  the  Santa  Mar- 
garita and  may  or  may  not  have  originated  at  the  same  time  as  the 
coarser  beds  in  the  Coalinga  field.  Fossils  found  a few  miles  to  the 
northwest,  in  Waltham  Valley,  indicate  that  the  shale  belongs  to  the 


38 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Santa  Margarita.  The  shale  may  be  a deep-water  equivalent  of  the 
coarser  sediments  in  the  Coalinga  field,  which  at  the  northern  end 
of  the  field  are  of  a strikingly  littoral  nature. 

Near  the  southeastern  end  of  Reef  Ridge  and  along  the  ridge  of 
the  Pyramid  Hills  northeast  of  Dudley  the  shale  has  a thickness  of 
from  1,050  to  1,200  feet.  It  is  divided  into  two  main  portions,  the 
lower  of  which  consists  of  harder,  more  siliceous,  and  more  thinly 
laminated  purple  and  white  shale,  and  the  upper  of  softer,  more 
argillaceous,  brownish  shale.  The  lower  portion  is  the  more  conspic- 
uous, constant,  and  typical;  the  upper  is  not  so  well  exposed,  is  more 
variable  in  character,  and  is  not  definitely  separable  from  the  soft 
sandstone  and  shale  of  the  formation  overlying.  The  following  sec- 
tion is  typical  of  the  formation  along  the  face  of  Reef  Ridge  at  its 
southeast  end,  the  different  zones  noted  not  being  sharply  separated 
from  one  another. 

Section  of  Santa  Margarita  formation  S\  miles  southeast  of  Big  Tar  Canyon. 

Feet. 

Soft,  brownish,  clay  shale  poorly  exposed,  grading  above  into  the  fine  sandy 
shale  at  the  base  of  the  Jacalitos  formation  and  below  into  bluish-purple  sili- 
ceous shale  with  occasional  hard,  more  siliceous  layers 400 

Hard,  siliceous,  porcelaneous,  thinly  bedded  shale,  lavender  colored,  but 
weathering  white,  with  prominent  iron  stain  throughout  along  joints;  break- 
ing with  angular  and  conchoidal  fracture  into  elongated,  sharp-edged  pieces; 


interbedded  with  occasional  soft  laminae 250 

Fairly  hard,  purplish,  siliceous  and  argillaceous  shale,  finely  fractured  into 
needle-like  fragments  with  yellow  calcareous  concretionary  lenses  and  inter- 
bedded porcelaneous  layers;  overlies  the  Vaqueros 400 


1,050 

The  two  lower  of  these  three  zones  differ  largely  in  the  proportion 
of  hard  beds  that  they  contain,  and,  as  this  proportion  is  variable  from 
place  to  place  they  do  not  form  continuous  belts  distinct  from  each 
other.  Together  they  make  up  the  lower  portion  of  the  formation 
according  to  the  division  given  above.  The  siliceous  shale  of  the 
lower  portion  varies  in  amount  of  induration,  ranging  from  a dull, 
opaque  rock  that  may  be  scratched  with  the  finger  nail  to  a sub- 
vitreous  flinty  variety  that  can  not  be  scratched  by  a knife.  It 
resembles  very  strongly  the  altered  varieties  of  shale  of  the  Monterey 
formation  (middle  Miocene)  that  occurs  nearer  the  Pacific  coast,  and 
the  shale  of  the  Tejon  and  the  “ Indicator”  bed  of  the  Vaqueros  of 
this  district.  Like  these,  its  less-altered  varieties  show  traces  of 
thickly  embedded  round  dots  and  flakes  that  are  almost  certainly  the 
remains  of  diatoms,  and  the  shale  has  the  characteristic  flaky  texture 
of  diatomaceous  material.  The  more  siliceous  shale  seems  to  be 
made  up  almost  entirely  of  the  crushed  diatom  tests.  It  contains 
also  fish  scales  and  other  particles  of  organic  origin,  but  almost  no 
molluscan  remains.  The  shale  laminae  are  locally  yellowish  and  cal- 


GEOLOGY. 


39 


careous  and  similar  to  the  foraminiferal  shale  of  the  Tejon.  Southeast 
of  Little  Tar  Canyon  the  formation  increases  in  thickness  to  about 
1,200  feet,  the  increase  being  mostly  in  the  brownish  shale  of  the  upper 
portion.  The  base  of  the  formation  is  approximately  at  the  axis  of 
the  anticline  of  the  Pyramid  Hills.  The  shale  appears  on  both 
sides  of  McLure  Valley  with  a general  steep  dip  toward  the  valley 
and  with  little  change  in  lithologic  character  or  thickness. 

The  northernmost  point  at  which  the  siliceous  shale  doubtfully 
ascribed  to  the  Santa  Margarita  formation  has  been  recognized  in  this 
district  is  at  the  northwest  end  of  Reef  Ridge,  where  the  white  shale 
forms  a thin  zone  between  the  underlying  and  overlying  sandstone 
formations.  It  has  a thickness  of  only  about  50  feet.  On  the  west 
side  of  Jasper  Canyon,  the  Vaqueros  is  overlain  by  hard,  brittle, 
yellowish-brown  and  black  clay  shale  that  may  be  a continuation 
of  the  Santa  Margarita,  but  its  relations  have  not  been  studied.  A 
zone  composed  in  large  part  of  shale  continues  in  the  same  position  in 
the  series  at  least  as  far  as  the  main  valley  of  Jacalitos  Creek,  to  the 
northwest.  This  zone  is  highly  tilted  and  much  broken  up. 

Southeastward  along  Reef  Ridge  the  shale  thickens  gradually  and 
continuously.  Southwest  of  the  head  of  Zapato  Creek  there  is  about 
200  feet  of  shale  that  is  divided  into  two  zones  of  about  equal  thick- 
ness. The  lower  one  is  of  siliceous  shale  weathering  purplish,  brown- 
ish, and  white,  similar  to  that  forming  the  prominent  outcrops  of  this 
formation  elsewhere.  The  upper  is  of  purplish  and  brownish  largely 
clay  shale.  This  grades  at  the  top  into  alternating  beds  of  brown 
sandstone  and  dark  clay  shale,  which  make  up  a thickness  of  several 
hundred  feet  and  which  may  or  may  not  be  a part  of  the  same  forma- 
tion. It  is  possible  that  this  sandstone  and  shale  correspond  to  part 
of  the  thickness  of  shale  found  farther  southeast,  but,  fossil  evidence 
being  lacking,  the  formation  is  restricted  for  the  present  to  the  beds 
that  are  purely  shale.  The  most  rapid  thickening  of  the  formation 
takes  place  between  Zapato  Canyon  and  Canoas  Canyon.  At  the 
latter  it  is  about  650  feet  thick  and  comprises  three  almost  equal 
zones — the  lowest  of  fine-grained  purplish  shale  of  medium  hardness, 
fractured  into  fine, needle-like,  angular  fragments;  the  middle  of  hard, 
siliceous  white  shale;  and  the  upper  of  soft  brownish  shale. 

The  same  siliceous  shale  is  found  south  of  the  Coalinga  district, 
extending  along  the  border  of  the  San  Joaquin  Valley.  It  thickens 
from  the  northwest  end  of  Reef  Ridge  toward  the  south  until  at  the 
Temblor  ranch,  in  western  Kern  County,  it  attains  the  remarkable 
thickness  of  5,400  feet.  It  is  probable  that  a part  of  the  formation 
here  stands  for  a period  of  time  not  represented  by  deposits  in  the 
region  of  Reef  Ridge  and  may  coincide  with  a part  or  all  of  the  Mont- 
terey  formation  (middle  Miocene).  The  thickening  of  the  shale  south- 
ward may  take  place  at  its  base,  the  beds  in  the  Coalinga  district 


40  ‘ COALTNGA  OIL  DISTRICT,  CALIFORNIA. 

representing  an  imoonformable  overlapping  of  the  upper  portion  upon 
the  Vaqueros. 

Importance  with  relation  to  petroleum. — In  the  Coalinga  field  the 
Santa  Margarita  formation  has  an  important  relation  in  different  ways 
to  the  occurrence  of  the  petroleum.  In  the  Eastside  field  its  base  is 
taken  as  extending  down  through  the  “Big  Blue.”  This  zone  caps 
the  Vaqueros  sandstone,  or  productive  zone;  and  although  small 
amounts  of  oil  and  tar  are  found  above  its  base,  there  is  none  in  com- 
mercial qualities.  The  Santa  Margarita  is  of  chief  importance  here 
as  forming  an  impervious  capping  which  has  held  the  oil  in.  In  the 
Westside  field  the  formations  are  thinner,  and  sand  beds  of  the  Santa 
Margarita  become  part  of  the  productive  zone.  In  the  Kreyenhagen 
field  the  shale  of  the  Santa  Margarita  acts,  as  the  “Big  Blue”  does, 
as  an  impervious  capping  that  keeps  the  oil  confined  within  the  Vaque- 
ros beds. 

JACALITOS  FORMATION  (EARLY  UPPER  MIOCENE). 

Definition  and  general  description. — The  formation  overlying  the 
Santa  Margarita  in  the  Kreyenhagen  Hills  consists  of  about  3,600  feet 
of  sand,  gravel,  clay,  and  sandstone,  in  places  very  fossiliferous,  and 
was  formed  in  the  earlier  upper  Miocene  time.  It  is  here  named  the 
Jacalitos  formation  owing  to  its  characteristic  exposures  both  north 
and  south  of  the  creek  of  that  name.  Abundant  and  well-preserved 
fossils,  by  means  of  which  its  age  is  determined,  occur  in  the  type 
locality.  It  is  probably  the  equivalent  of  parts  of  one  or  more  of  the 
upper  Miocene  formations  known  in  other  parts  of  the  State,  but  its 
definite  relations  to  these  have  not  yet  been  worked  out.  It  is  in 
part  represented  in  the  northern  portion  of  the  district  by  similar  beds 
aggregating  a much  smaller  thickness. 

In  the  fields  this  formation  does  not  stand  out  prominently  as  a 
lithologic  or  stratigraphic  unit  and  is  not  readily  distinguishable  by 
itself.  On  the  contrary,  it  forms  merely  a portion  of  the  great  thick- 
ness of  apparently  conformable  Tertiary  beds  that  are  exposed  in  the 
great  monocline,  dipping  at  medium  and  high  angles  toward  the  valley. 
The  formation  may  be  roughly  distinguished  as  that  portion  of  the 
series  between  the  shale  of  the  Santa  Margarita  below  and  the  major 
beds  of  blue  sand  that  are  characteristic  of  the  lower  part  of  the  forma- 
tion above  it  (the  Etchegoin)  throughout  the  district.  The  Jacalitos, 
however,  includes  a great  thickness  of  blue-sand  beds  at  its  summit  in 
the  southeastern  part  of  the  Kreyenhagen  Hills.  A feature  of  this 
formation  is  the  occurrence  at  intervals  in  it  of  hard  zones  that  project 
like  saw  teeth  and  by  their  resistance  protect  the  beds  immediately 
above  and  below  them,  thus  forming  long  parallel  ridges.  The  same 
feature  is  in  a greater  measure  characteristic  of  the  Vaqueros  sandstone 
and  Santa  Margarita  formation  below  and  less  so  of  the  Etchegoin 


GEOLOGY. 


41 


(uppermost  Miocene)  formation  above.  Another  feature  of  the  Jaca- 
litos  is  the  great  number  of  sand  and  pebble  beds,  full  of  sea  urchins, 
that  are  found  in  all  parts  of  the  formation.  This  feature  is  likewise 
one  belonging  to  the  formation  above.  The  most  important  features, 
however,  and  the  only  t>nes  that  can  be  relied  upon  to  separate  the 
Jacalitos  from  the  other  sandy  formations,  are  the  position  that  it 
occupies  in  the  series  and  the  various  fossils  that  it  contains. 

The  Jacalitos  in  the  Kreyenhagen  Hills  is  probably  unconformable 
with  the  Santa  Margarita  below,  although  the  two  formations  appear 
conformable  at  the  contact,  the  line  between  them  being  arbitrarily 
drawn  where  the  beds  that  are  predominantly  shale  (Santa  Margarita) 
give  place  to  sandy  beds  (Jacalitos).  In  the  northern  part  of  the 
district  the  relation  of  these  two  formations  appears  also  to  be  one 
of  conformity,  although  the  overlap  of  the  Jacalitos  on  the  Santa 
Margarita  near  Oil  Canyon  proves  clearly  that  it  is  the  opposite.  The 
line  there  also  is  drawn  arbitrarily  at  the  base  of  the  prominent  pebble 
zone  full  of  fossil  wood.  The  Jacalitos  is  likewise  conformable  to  all 
appearances  with  the  later  Miocene  (Etchegoin)  beds  which  rest  above 
it  and  are  largely  similar  in  composition,  the  line  between  these  two 
formations  being  likewise  drawn  somewhat  arbitrarily,’  chiefly  on  the 
basis  of  the  fossil  contents.  There  is  a possibility  that  an  uncon- 
formity between  these  two  formations  exists  in  the  hills  surrounding 
Pleasant  Valley-.  (See  p.  49.) 

From  its  locality  of  typical  occurrence  in  the  KreyTenhagen  and 
Jacalitos  hills  the  Jacalitos  formation  extends  south  westward  into 
McLure  Valley,  where  it  occupies  a similar  position  between  the  under- 
lying Santa  Margarita  and  the  overly-ing  Pliocene  sands.  Toward  the 
northwest  it  reaches  into  the  interior  of  the  Diablo  Range  through 
the  depression  formed  by  the  Waltham  syncline  and  toward  the  north 
extends  across  Alcalde  Canyon  into  the  region  around  Pleasant  Valley-. 
North  of  Jacalitos  Creek  it  no  longer  rests  upon  the  shale  of  the  Santa 
Margarita,  that  formation  being  lacking,  and  the  Jacalitos  ceases  to  be 
completely  represented.  The  question  of  the  relations  of  the  beds  of 
this  age  in  the  northern  and  southern  portions  of  the  district  is  com- 
plex and  can  be  decided  only  on  the  basis  of  detailed  paleontologic 
evidence.  The  formation  will  be  considered  separately  for  the  areas 
lying  to  the  south  and  to  the  north  of  Waltham  Creek. 

South  of  Waltham  Creek . — From  Jacalitos  Creek  southward  the 
Jacalitos  formation  affords  more  complete  exposures  than  elsewhere. 
The  type  locality-  for  its  fossils  is  along  that  creek,  near  which  repre- 
sentative faunas  have  been  collected  at  several  different  points  from 
different  horizons,  but  the  undisturbed  monocline  in  the  range  of  the 
Kreyenhagen  Hills  furnishes  somewhat  better  sections  of  the  forma- 
tion as  a whole,  since  it  has  suffered  considerable  disturbance  along 
Jacalitos  Creek  and  in  the  hills  north  of  it.  Moreover,  in  the  latter 


42 


flOALINGA.  OIL  DISTRICT,  CALIFORNIA. 


region  the  base  of  the  formation  does  not  appear  within  the  area 
shown  on  the  map  and  has  not  been  definitely  traced.  As  before 
stated,  the  alternating  beds  of  brown  sandstone  and  dark  shale  that 
overlie  the  siliceous  shale  of  the  Santa  Margarita  about  the  head  of 
Zapato  Creek  and  thence  westward  are  mapped  with  the  Jacalitos, 
although  it  is  uncertain  to  which  formation  they  properly  belong. 

The  following  tabulated  sections  will  give  the  best  description  of 
the  lithologic  character  of  the  Jacalitos  formation  and  its  zones.  It 
must  be  borne  in  mind,  however,  that  the  formation  is  variable  from 
place  to  place;  that  any  single  description  applies  merely  to  a single 
locality;  that  the  different  zones  noted  are  not  sharply  separable,  but 
grade  into  one  another,  all  containing  elements  in  minor  quantity 
common  to  the  others,  and  that  a great  variety  of  sedimentary  beds 
occur  that  would  necessitate  almost  endless  discussion  to  describe  in 
detail.  Although  the  formation  is  thus  variable,  part  of  the  variation 
noticeable  in  the  sections  may  be  due  to  the  fact  that  exposures  are 
not  complete  and  that  beds  and  fossils  apparent  in  one  place  are  fre- 
quently hidden  in  others.  It  is  especially  difficult  to  determine  the 
relative  quantitative  importance  of  clay  or  somewhat  compacted  shale, 
for  the  reason  that  the  firmer  sand  beds  are  better  exposed  and  there- 
fore appear  to  dominate,  and  because  it  can  not  always  be  determined 
whether  the  softer  unexposed  beds  are  fine  sand  or  clay. 

The  following  is  a section  of  the  Jacalitos  along  Jacalitos  Creek, 
from  the  summit  of  the  formation,  at  a point  on  the  south  side  of  the 
creek  and  at  the  north  base  of  the  1,220-foot  hill  in  the  eastern  part 
of  sec.  31,  T.  21  S.,  R.  15  E.,  to  its  contact  with  the  prominent  Vaque- 
ros  sandstone  at  a point  not  shown  on  the  map,  about  I J miles  west- 
northwest  of  the  end  of  Reef  Ridge,  in  the  middle  of  sec.  11,  T.  22  S., 
R.  14  E. 


Section  of  Jacalitos  formation  on  Jacalitos  Creek. 

Bluish  to  brownish-gray  clay  and  clayey  sand,  alternating  with  light-gray  and 
olive-gray  pebbly  sand,  with  occasional  hard  fossil  layers  and  with  Pecten 
estrellanus  bed  at  base ; overlain  by  blue  sand  at  the  base  of  the  Etchegoin . . 
Massive  beds  of  buff  and  olive-gray  sandstone  and  sandy  clay  interbedded 
with  thin  and  thick  beds  of  olive-gray  pebbly  sandstone  and  gravel,  and 
occasional  sandstone  layers.  Sand  dollars  ( Echinarachnius ) numerous 
throughout,  usually  in  the  pebbly  layers.  Bed  of  dark-brown  sandstone 
at  base  (at  forks  of  Jacalitos  and  Jasper  creeks),  containing  a rich  fauna, 

including  Chione,  Macoma,  Panopea,  Echinarachnius,  etc 

Alternating  heavy  beds  of  coarse  gray  and  brown  sandstone  and  thin  beds  of 
fine  sandstone  and  sand  of  the  same  colors,  with  some  beds  of  gritty  olive- 
gray  sandstone  and  hard  fossil  layers.  Bed  with  large  Astrodapsis  200  feet 

above  base.  Probably  the  zone  of  Trophon  found  farther  southeast 

Alternating  beds  of  grayish  and  brownish  sand  and  sandstone,  with  some  sandy 

clay  and  fossil  layers  in  the  sandstone 

Alternating  beds  of  soft  gray  and  brown  shale  and  sandstone,  much  tilted  and 
fractured,  and  in  part  overturned 


Feet. 


750 


1,300 


500 


750 


500+ 


3,  800+ 


GEOLOGY. 


48 


The  basal  portion  of  this  section  rests  upon  the  continuation  of  the 
steeply  tilted  Yaqueros  sandstone  that  is  so  prominent  on  the  face  of 
Reef  Ridge.  Shale  similar  to  the  typical  shale,  mapped  as  Santa 
Margarita,  is  entirely  lacking;  but  it  is  possible  that  the  much 
disturbed  basal  zone  of  this  section  is  the  equivalent  of  that  shale. 
It  may  be  the  continuation  of  the  similar  thickness  of  alternating 
beds  of  brown  sandstone  and  dark  shale  overlying  the  typical  shale 
of  the  Santa  Margarita  along  Zapato  Creek,  which  has  been  mentioned 
(p.  42)  as  doubtfully  referred  to  the  Jacalitos  instead  of  to  the  Santa 
Margarita  formation.  There  is  a possibility  that  this  zone  of  alter- 
nating beds,  which  is  for  the  present  considered  as  the  basal  portion 
of  the  Jacalitos,  may  be  unconformable  with  the  main  body  of  that 
formation,  but  further  work  will  be  required  in  order  to  determine 
this. 

The  middle  portion  of  the  Jacalitos  formation,  m this  locality  espe- 
cially, contains  large  unconsolidated  accumulations  of  fine  pebbles, 
some  in  thick  beds  by  themselves  and  some  interbedded  in  thin  layers 
in  the  sand  beds  or  scattered  throughout  the  sand.  These  coarse  beds 
are  frequently  fossiliferous,  and  sand  dollars  are  especially  abundant 
in  them. 

The  uppermost  beds  of  the  above  section  underlie  the  lowest  of  a 
number  of  prominent  blue-sand  beds  that  are  characteristic  of  the 
landscape  in  this  district  along  the  belt  of  Etchegoin  (Pliocene)  for- 
mation. The  line  of  contact  between  the  Jacalitos  and  Etchegoin 
formations  is  drawn  somewhat  arbitrarily  on  the  basis  of  this  litho- 
logic break  and  of  the  characteristic  Mytiloconcha  and  Glycymeris  fauna 
that  occurs  in  a bed  just  above.  The  beds  above  and  below  this  line 
of  contact  dip  with  perfect  conformity  at  an  angle  of  about  25°. 

The  following  is  a section  along  Canoas  Creek  from  the  top  of  the 
Jacalitos,  immediately  south  of  the  house  of  Hugo  Kreyenhagen,  to 
its  contact  with  the  Santa  Margarita: 

Section  of  Jacalitos  formation  along  Canoas  Creek. 

Feet. 

Chiefly  grayish  sand  and  soft  sandstone,  with  thick  pebbly  zone  containing 


Pecten  estrellanus  at  base;  fossil  bed  with  Cardium,  Solen,  Echinarachnius, 

Macoma,  Nassa,  Olivella,  etc.,  at  top 650 

Chiefly  massive  gray  and  buff-colored  coarse-grained  sand;  a prominent  bed 

of  friable  dark  sandstone  with  Panopea , etc.,  at  base 1,  000 

Similar  sand,  with  prominent  ridge-forming  bed  at  base 350 

Similar  sand,  with  prominent  bed,  the  zone  of  Trophon,  etc.,  at  base 400 

Similar  sand,  with  occasional  sandstone  layers  and  with  prominent  sandstone 

bed  at  base,  forming  first  hill  northeast  of  Reef  Ridge 500 

Similar  sand,  grading  below  into  sandy  shale,  overlying  the  Santa  Margarita 600 


3,  500 

Southeast  of  Canoas  Creek  the  Jacalitos  formation  preserves  a char- 
acter and  thickness  very  similar  to  that  given  in  the  above  sections. 


44 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


The  fossiliferous  sandstone  beds  become  more  indurated,  so  that  they 
stand  out  like  sawteeth  on  the  summits  of  longitudinal  ridges  most  of 
the  way  to  Big  Tar  Canyon  and  form  very  pronounced  features  of  the 
landscape.  As  this  canyon  is  approached  the  beds  assume  steeper 
and  steeper  attitudes  until  they  dip  uniformly  at  angles  varying 
between  50°  and  60°.  The  chief  new  feature  assumed  by  the  forma- 
tion in  this  region  is  that  some  of  the  sand  and  pebble  beds  in  its 
higher  portion  have  the  blue  color  characteristic  of  the  basal  beds  of 
the  Etchegoin.  Confusion  is  thus  introduced  into  the  separation  of 
the  two  formations,  but  the  same  paleontologic  criteria  used  in  dis- 
tinguishing them  elsewhere  still  hold  good  here.  In  the  neighborhood 
of  Garza  and  Big  Tar  creeks  the  zone  of  blue  sands  extends  down  over 
800  feet  into  the  Jacalitos,  whereas  farther  southeast,  as  shown  in  the 
next  section,  it  extends  to  a still  lower  horizon,  the  lowest  at  which  it 
has  been  found  anywhere.  The  exact  similarity  of  the  beds  above 
and  below  the  contact  of  this  formation  with  the  overlying  Etchegoin, 
together  with  their  perfect  angular  conformity,  is  almost  conclusive 
evidence  of  their  actual'  conformity  and  continuity. 

Southeast  of  Big  Tar  Creek  the  beds  begin  to  lose  prominence  and 
to  form  nearly  uniform  rolling  hills  of  soft  sand,  with  few  large  expo- 
sures. The  dip  in  this  region  becomes  uniformly  about  60°.  The 
following  section  shows  the  character  of  the  formation  at  about  the 
farthest  point  southeast  in  the  Kreyenhagen  Hills  at  which  a sec- 
tion of  satisfactory  completeness  can  be  obtained  from  the  surface 
exposures : 

Section  of  Jacalitos  formation  on  north  side  of  Reef  Ridge  3\  miles  southeast  of  Big  Tar 


Dark-gray  sand  with  about  20  feet  of  light-blue  sand  at  base 120 

Olive-gray  sand  with  light-blue  sand  at  base ; the  basal  portion  is  probably  the 

main  Pecten  estrellanus  zone  found  1 mile  northeast 350 

Fine  shaly  yellowish-gray  sand,  with  whitish-gray  and  dark-gray  layers  inter- 

bedded  and  some  bluish  pebbly  sand;  the  lowest  blue  sand  is  at  base 720 

Compact,  medium-grained  to  coarse  gray  sand,  like  beach  sand 275 

Olive-gray  speckled  sand  and  soft  sandstone  with  appearance  of  a pepper-and- 

salt  mixture 275 

Interbedded  fine  and  medium  grained  grayish,  whitish,  and  yellowish  sand 

and  speckled  sand  like  the  last,  with  some  clay  layers GOO 

Fine  and  medium  grained  reddish,  yellowish,  and  grayish  sand  and  soft  sand- 
stone with  white  sandy  clay  at  top  and  coarse  pebbly  sand  300  feet  below  top; 
grading  at  base  into  soft  whitish -gray  sandy  shale 1,  200 


3,  540 

The  Jacalitos  is  worn  off  over  the  summit  of  the  Pyramid  Hills 
anticline  but  reappears  on  its  southwestern  flank  on  the  north  side  of 
McLure  Valley,  dipping  under  the  alluvium  of  the  valley  floor.  The 
descriptions  of  the  formation  already  given  apply  to  it  as  it  appears 
in  this  region.  The  exposures  are  in  general  poor. 


GEOLOGY. 


45 


The  succession  of  beds  exposed  on  the  western  flank  of  the  high 
hill  1 mile  southeast  of  Alcalde,  east  of  the  road  leading  southward 
from  Alcalde  toward  Jacalitos  Creek,  comprises  about  1,600  feet  of 
sand,  clay,  gravel,  and  fossiliferous  sandstone  up  to  the  base  of  the 
blue  beds  that  mark  the  Etchegoin  formation.  Locally,  on  the  flank 
of  this  hill  the  beds  have  a slight  stain  resembling' that  due  to  the 
presence  of  oil.  West  of  this  road  above  mentioned  the  Jacalitos  beds 
are  chiefly  sand,  with  some  clay  and  gravel  and  with  fossils.  They 
overlap  upon  the  steepty  tilted  Cretaceous  strata  and  are  warped  into 
a number  of  low  plunging  folds.  Still  farther  west  the  Jacalitos  over- 
laps a wide  extent  of  country  in  the  Waltham  syncline,  along  which 
it  has  been  traced  6 miles  west  of  the  area  shown  on  the  map  along 
Jacalitos  Creek  as  far  as  the  road  to  Stone  Canyon. 

Alcalde  Hills. — North  of  Waltham  Creek  the  Jacalitos  formation 
loses  the  great  thickness  that  characterizes  it  throughout  its  occur- 
rence to  the  south,  retaining  a thickness  of  only  about  800  feet.  This 
thinning  takes  place  very  rapidly  in  the  immediate  vicinity  of  Wal- 
tham Creek,  as  it  does  in  the  case  of  the  Etchegoin  formation  as  well, 
indicating  that  the  lower  portion  of  Alcalde  Canyon  follows  a line  that 
has  been  an  extremely  important  locus  of  orogenic  movements.  The 
areas  to  the  north  and  south  thus  separated  have  had  in  large  measure 
a different  geologic  history.  The  exact  nature  of  the  thinning  that 
takes  place  in  the  Jacalitos  has  not  been  determined;  whether  it  is  a 
constant  thinning  affecting  all  of  the  beds  of  the  formation  or  whether 
it  is  due  to  the  absence  of  some  large  parts  of  the  formation,  owing 
either  to  their  having  never  been  deposited  north  of  Waltham  Creek 
or  to  their  having  been  worn  away,  is  not  known  at  present.  It  is 
believed  that  the  area  north  of  Waltham  Creek  was  land  during  the 
earlier  part  of  Jacalitos  time  and  that  the  lower  portion  of  the  forma- 
tion was  never  deposited  there. 

The  formation  over  the  area  of  the  Alcalde  Hills  retains  the  general 
character  of  the  beds  to  the  south.  It  is  a variable  formation  of  inco- 
herent yellow,  brown,  and  gray  sand,  sandstone,  clay,  and  gravel, 
locally  containing  fossils  such  as  Pecten  estrellanus , Pecten  oweni,  a 
large  species  of  Metis , and  a large  sand  dollar  of  the  genus  Echinarach- 
nius.  The  typical  fauna  of  the  lower  part  of  the  formation  in  the 
type  locality  along  Jacalitos  Creek  is  not  present.  The  beds  are 
evidently  of  near-shore  origin,  being  in  many  places  roughly  bedded, 
cross-bedded,  and  variable.  They  are  full  of  gypsum.  The  base  of 
the  formation  as  mapped  is  a fossiliferous  bed,  containing  Pecten  estrel- 
lanus, and  other  fossils,  that  is  traceable  southward  from  the  San 
Joaquin  coal  mine  to  Waltham  Creek.  It  is  underlain,  conformably 
so  far  as  known,  by  a zone  of  clay  and  fine  sand  about  300  feet  thick, 
which  has  been  mentioned  before  (p.  37)  as  possibly  belonging  to  the 
Santa  Margarita  but  which  is  mapped  with  the  Vaqueros.  The  sum- 
mit of  the  Jacalitos  formation  is  mapped  at  the  base  of  the  Glycymeris 


46 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


zone,  which  is  the  equivalent  of  the  basal  Etchegoin  as  found  elsewhere. 
The  relation  of  the  beds  along  this  contact  is  also  conformable  so  far 
as  observed.  A section  of  this  and  the  associated  formations  will  be 
found  on  page  101. 

North  of  Pleasant  Valley . — The  beds  correlated  with  the  Jacalitos 
in  the  northern  part  of  the  district  form  that  part  of  the  series  on 
Joaquin  Ridge  which  lies  between  a prominent  zone  of  gravel  at  the 
base  that  outcrops  typically  on  the  hill  (where  the  tanks  are  situated 
above  the  Standard  Oil  Company’s  wells,  on  the  west  side  of  the  NE.  \ 
sec.  28,  T.  19  S.,  R.  15  E.)  and  the  base  of  a zone  of  gray  sand  with 
abundant  fossils  outcropping  typically  on  the  hill  where  one  tank 
stands,  in  the  NE.  \ SW.  } sec.  34,  T.  19  S.,  R.  15  E.  This  portion  of 
the  series  consists  of  about  1,600  feet  of  alternating  fine  gray  sand  and 
clay,  pebbly  and  medium-grained  sand  and  sandstone,  and  gravel. 
The  basal  pebbly  zone  has  a thickness  of  about  150  feet,  of  which  the 
lower  half  is  a solid  layer  of  pebbly  gravel,  locally  hardened  to  con- 
glomerate, and  the  upper  half  thin-bedded,  brown,  gray,  and  in  some 
places  pinkish,  sandstone  and  sand  intermingled  with  pebbles  and 
with  occasional  shaly  layers.  This  zone  contains  a great  abundance 
of  petrified  wood  in  large  fragments,  and  at  one  place  a tooth  of  an 
extinct  species  of  horse  was  found  in  it.  The  rest  of  the  formation 
is  mostly  soft,  fine  sand,  with  which  hard  sandstone  layers,  pebbly 
sand,  and  sandy  clay  beds  are  frequently  interbedded.  Several 
pebbly  zones  have  considerable  thickness,  but  no  part  of  the  upper 
portion  has  distinct  individuality  or  prominence,  and  very  few  fossils 
have  been  found  in  it. 

Importance  with  relation  to  petroleum. — The  Jacalitos  formation  is 
not  petroliferous  in  the  Eastside  field  in  the  northern  part  of  the 
district,  but  is  very  productive  in  the  Westside  field  owing  to  the 
thinning  out  of  the  formations  between  it  and  the  Tejon.  In  the 
Kreyenhagen  field  it  is  not  known  to  be  productive  at  any  point,  no 
oil  having  escaped  from  the  Tejon  and  Vaqueros  through  the  shales 
of  the  Santa  Margarita.  The  thickness  and  character  of  the  Jacalitos 
throughout  the  district  have  an  important  bearing  on  the  question  of 
the  accessibility  of  the  oil,  owing  to  the  fact  that  most  of  the  wells 
have  to  penetrate  it  in  order  to  reach  the  oil  sands  at  depths  at  which 
they  will  be  productive.  A knowledge  of  its  thickness  has  been 
especially  useful  in  making  calculations  as  to  the  depth  at  which  the 
oil  sands  may  be  found  in  the  Kreyenhagen  and  Kettleman  hills. 

ETCHEGOIN  FORMATION  (UPPERMOST  MIOCENE). 

Definition  and  general  description. — The  name  Etchegoin  was 
applied  by  F.  M.  Anderson a to  a great  thickness  of  beds  of  unconsoli- 


a Anderson,  F.  M.,A  stratigraphic  study  in  the  Mount  Diablo  Range  of  California:  Proc.  Cali- 
fornia Acad.  Sci.,  3d  ser.,  vol.  2,  No.  1, 1905. 


GEOLOGY. 


47 


dated  sand,  gravel,  and  clay,  characteristically  blue  at  the  base,  occur- 
ring typically  in  the  vicinity  of  the  Etchegoin  ranch,  20  miles  north 
of  Coalinga,  and  extending  continuously  from  there  both  northwest 
and  southeast  along  the  border  of  the  Diablo  Range.  In  accordance 
with  Mr.  Anderson’s  statements  and  on  the  basis  of  the  reasons  stated 
below  the  Etchegoin  formation  is  mapped  and  described  in  the  pres- 
ent paper  as  the  succession  of  slightly  consolidated  beds  of  sand, 
gravel,  and  clay  occurring  on  the  summit  and  flanks  of  Anticline 
Ridge  and  on  the  southeast  end  of  Joaquin  Ridge  north  of  Coalinga, 
above  the  base  of  the  hill-forming  sandstone  beds  (referred  to  for 
convenience  as  the  Glycymeris  zone),  and  below  the  beds  described 
as  the  Paso  Robles  formation.  Strata  in  other  portions  of  the 
Coalinga  district  are  referred  to  the  Etchegoin  formation  on  the  basis 
of  paleontologic  correlation  with  the  beds  on  Anticline  Ridge. 

The  Glycymeris  zone  is  an  extremely  fossiliferous  bed  of  somewhat 
indurated  sand  that  forms  the  summit  of  the  hill  at  the  northwest 
end  of  Anticline  Ridge  (in  the  NW.  \ SW.  J sec.  34,  T.  19  S.,  R.  15  E.) 
and  extends  continuously  from  that  point  along  the  line  mapped  as 
the  base  of  the  Etchegoin  formation.  It  is  underlain  at  the  locality 
referred  to  by  clay  that  is  classed  in  the  Jacalitos  formation  and  is 
overlain  by  a thick  succession  of  bluish-gray  sand  beds  interbedded 
with  dark-gray  sand.  The  zone  affords  almost  perfect  specimens  of 
many  species  of  fossils  that  make  up  a distinctive  fauna.  It  is  called 
the  Glycymeris  zone  for  ease  of  reference,  because  it  is  an  important 
datum  line  that  may  be  recognized  by  the  association  of  fossils  con- 
tained in  it. 

There  are  various  reasons  for  assuming  this  zone  to  be  the  base  of 
the  formation.  First,  an  unconformity  is  known  to  occur  below  it 
in  the  synclinal  basin  north  of  White  Creek,  for  there  a zone  contain- 
ing the  same  fauna  rests  directly  upon  Cretaceous  (Chico)  sandstone, 
and  somewhere  between  Oil  Canyon  and  the  Cretaceous  area  an 
unconformable  overlap  of  the  Glycymeris  zone  upon  the  underlying 
Tertiary  beds  must  exist.  It  is  therefore  appropriate  to  consider 
the  beds  above  the  base  of  the  Glycymeris  zone  as  a distinct  forma- 
tion, although  on  Anticline  Ridge  and  in  the  greater  portion  of  their 
extent  in  the  region  north  of  Coalinga,  as  well  as  to  the  south  as  far 
as  they  have  been  studied,  they  appear  to  rest  conformably  upon  the 
beds  below.  A further  reason  for  assuming  this  zone  as  the  base  is 
that  it  is  at  the  bottom  of  a succession  of  bluish  sand  beds  on  Anti- 
cline Ridge  and  at  some  other  places  in  the  Coalinga  district,  thus 
marking  a sharp  and  easily  recognizable  variation  in  lithology  between 
the  beds  below  and  above  it.  At  other  places,  however,  especially 
in  the  southern  portion  of  the  Kreyenhagen  Hills,  the  blue  sands 
occur  also  far  below  the  Glycymeris  zone,  so  that  the  lithologic  feature 
can  not  be  relied  upon  everywhere  as  a basis  of  separation. 


48 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


In  the  description  of  the  Jacalitos  (early  upper  Miocene)  frequent 
reference  has  been  made  to  the  overlying  Etchegoin  (late  upper  Mio- 
cene). In  fact,  these  formations  are  so  closely  related  and  so  similar 
that  the  one  can  not  well  be  described  without  reference  to  the  other. 
In  places  they  seem  to  have  originated  as  a chronologically  contin- 
uous succession  of  marine  deposits  and  are  only  arbitrarily  separable, 
whereas  in  other  places  an  overlap  of  the  latter  upon  the  former  has 
taken  place.  Many  of  the  features  of  structure,  influence  on  topog- 
raphy, and  lithologic  variability  mentioned  in  connection  with  the 
former  exist  also  in  the  latter. 

The  Etchegoin  formation  consists  of  slightly  consolidated  sand, 
clay,  and  gravel,  interbedded  with  occasional  indurated  beds,  and  is 
characterized  by  an  abundance  of  invertebrate  fossils,  among  which 
a few  forms  like  sand  dollars  (Echinarachnius) , barnacles  ( Balanus ), 
Mulinia,  Area,  My  a,  small  oysters,  Neverita,  etc.,  are  particularly 
prevalent.  It  reaches  a thickness  of  over  3*, 500  feet  in  the  southern 
portion  of  the  district,  but  in  the  northern  portion  it  is  at  most  only 
half  as  thick.  It  may  be  most  easily  recognized  by  the  dominant 
grayish-blue  color  of  the  massive  sand  beds  that  comprise  a thickness 
of  several  hundred  feet  at  its  base,  but  an  examination  of  its  charac- 
teristic fossils  is  the  only  means  of  distinguishing  it  accurately  from 
the  associated  formations. 

One  of  the  most  important  of  its  broad  features  in  the  Coalinga 
district  is  the  usual  predominance  of  coarse  material,  such  as  sand 
and  pebbly  deposits,  in  its  lower  portion,  and  of  finer  material,  such 
as  extremely  fine  sand  and  clay,  in  its  upper  portion;  but  this  feature 
is  characteristic  in  various  degrees  according  to  the  locality,  and  in 
some  places  is  hardly  noticeable. 

Coalinga  field. — In  the  oil  field  north  of  Coalinga  the  Etchegoin  has 
a thickness  of  about  1,700  feet.  The  basal  Glycymeris  zone  has 
already  been  described.  Several  other  fossiliferous  beds  occur 
within  several  hundred  feet  above  this,  and  contain  abundant  sand 
dollars  (EcdiinaracJinius) , barnacles  {Balanus),  cardiums,  turritellas, 
etc.  The  lower  portion  of  the  formation  is  composed  largely  of  beds 
of  compact  coarse  and  fine  blue  sand  alternating  with  zones  of 
pebbly  sand,  fine  gray  sand,  and  some  clay,  with  occasional  more 
hardened  beds.  The  clay  increases  toward  the  upper  part  of  the 
formation,  being  interbedded  with  unconsolidated  light-gray  sand 
that  spreads  over  the  surface  and  obscures  the  structure.  The  forma- 
tion occurs  in  the  low  hills  bordering  the  valley  and  passes  beneath 
the  alluvium  of  the  floor. 

The  Etchegoin  forms  a belt  along  the  edge  of  the  Alcalde  Hills  west 
of  Coalinga  and  is  overlapped  by  the  recent  valley  deposits.  A good 
section  of  it  is  obtainable  2 miles  southwest  of  Coalinga,  where  the 
fossiliferous  beds  of  the  Glycymeris  zone  at  its  base  outcrop  on  the 


GEOLOGY. 


49 


west  side  of  the  summit  of  a prominent  hill  on  which  a tank  is  situated, 
in  the  SE.  \ sec.  1,  T.  21  S.,  R.  14  E.  These  beds  ere  of  yellowish 
gypsiferous  sand  and  sandstone  of  fine  to  medium  grain,  with  a 
thickness  of  about  200  feet.  They  are  overlain  on  the  top  of  the  hill 
by  200  feet  of  both  loose  and  indurated  coarse  gravel,  pebbly  sand, 
and  interbedded  fine  sand  containing  sand  dollars.  Above  these 
beds  comes  a thickness  of  250  feet  of  whitish-gray  sand  of  the  tex- 
ture of  granulated  sugar,  grading  at  the  base  into  coarser  even- 
grained sand.  This  zone  is  followed  above  by  about  20  feet  of  coarse 
sand,  sandstone,  and  pebble  conglomerate  containing  many  fossils, 
including  Pecten  wattsi,  Area,  Ostrea  (small),  sand  dollars,  sea  urchins 
(Astrodapsis) , etc.  This  is  the  zone  of  Pecten  coalingaensis  that 
occurs  in  the  Kettleman  and  Kreyenhagen  hills.  (See  p.  50.)  The 
highest  beds  exposed  are  of  fine  yellowish  and  whitish-gray  sand 
comprising  a thickness  of  about  50  feet,  these  being  overlain  by  the 
surface  deposits  at  the  base  of  the  hills.  The  thickness  of  the  forma- 
tion in  this  section  is  about  700  feet,  but  as  the  uppermost  beds  that 
belong  above  the  Pecten  coalingaensis  zone  are  hidden,  the  whole 
formation  probably  has  a thickness  of  about  900  or  1,000  feet. 

White  Creek  basin. — A detached  area  of  Etchegoin  beds  is  pre- 
served in  the  syncline  near  the  head  of  White  Creek,  northwest  of 
Coalinga,  where  the  formation  rests  upon  the  beds  of  the  Cretaceous 
(Chico).  At  one  time  these  beds  were  doubtless  continuous  with 
those  of  the  same  formation  around  Pleasant  Valley,  and  their  pres- 
ence in  this  interior  basin  proves  that  an  extended  overlap  of  the 
Etchegoin  over  the  older  Tertiary  formations  and  onto  the  Creta- 
ceous took  place. 

The  basal  beds  appearing  above  the  Cretaceous  in  this  syncline 
are  very  fossiliferous  and  contain  a finely  preserved  fauna  exactly 
similar  to  that  of  the  Glycymeris  zone  on  Anticline  Ridge.  They 
may  be  regarded  as  representing  the  same  horizon.  The  lowest  100 
feet  of  beds  immediately  overlying  the  Cretaceous  are  composed  of 
coarse  and  pebbly,  compact  but  soft,  yellowish-gray  sandstone 
hardly  distinguishable  from  the  underlying  Cretaceous  sandstone. 
These  beds  are  not  very  fossiliferous,  but  grade  upward  into  beds 
largely  composed  of  fossils,  with  a matrix  of  yellowish-gray  sand. 
Area  is  the  most  abundant  genus,  but  Glycymeris,  sand  dollars 
(Echinarachnius) , and  locally  many  other  forms  are  also  very  abun- 
dant. The  bulk  of  the  formation  in  its  middle  portion  consists  of 
similar  sand  and  sandstone  resembling  the  massive  upper  Cretaceous 
sandstone  and  containing  occasional  fossil  beds.  Numerous  layers 
of  very  hard  sandstone  and  some  concretions  are  present.  The  beds 
for  a few  hundred  feet  below  the  top  of  the  formation  are  more  varia- 
ble, a thick  zone  of  coarse  pebbles  being  followed  above  by  alter- 
nating beds  of  sandy  shale,  calcareous  shale,  and  coarse  and  fine  sand 
52332— Bull.  357—08 4 


50 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


and  sandstone,  and,  near  the  top,  a hard  and  prominent  thin  bed  of 
dark-brownish  sandstone  full  of  small  white  fossils.  The  total  thick- 
ness of  the  formation  is  about  1,100  feet,  which  corresponds  fairly  well 
with  the  thickness  that  it  is  supposed  to  possess  in  the  hills  west  of 
Pleasant  Valley. 

Kreyenhagen  Hills. — The  best  and  most  complete  sections  of  the 
Etchegoin  may  be  found  in  the  Kreyenhagen  Hills,  where  the 
upturned  northeastward-dipping  beds  of  this  formation  are  exposed 
as  a belt  in  the  foothill  area  between  the  Jacalitos  and  the  Paso 
Kobles.  It  is  not  easily  separable  from  these  two  formations,  the 
line  at  the  base  being  especially  arbitrary.  The  contact  at  the  base 
of  the  Etchegoin  is  drawn  below  a fairly  constant  fossiliferous  zone, 
supposed  to  be  the  equivalent  of  the  Glycymeris  zone  north  of  Coalinga. 
The  contact  at  the  top  of  the  formation  is  marked  by  the  usual  occur- 
rence above  it  of  the  gravelly  beds  of  the  Paso  Robles,  by  the  pres- 
ence at  the  top  of  a zone  containing  My  a,  Ostrea,  etc.,  which  may  be 
called  the  upper  Mya  zone,  and  by  other  more  local  criteria. 

The  zone  of  blue-sand  beds  at  the  base  of  the  formation  is  constant 
throughout  the  Kreyenhagen  Hills.  Its  thickness  is  variable  from 
place  to  place  and  is  of  little  value  except  for  broad  correlations. 
The  lower  part  of  the  formation  is  composed  chiefly  of  sandy  beds  of 
all  degrees  of  coarseness  up  to  pebble  beds,  and  of  many  varieties  of 
blue,  gray,  and  drab  color,  with  minor  amounts  of  clay.  The  upper 
part  of  the  formation  is  composed  of  alternating  thick  zones  of  sand 
and  clay,  the  amount  of  clay  being  somewhat  greater  than  in  the 
lower  portion. 

There  are  four  main  fossil  zones  in  the  Etchegoin  of  the  Kreyen- 
hagen Hills,  corresponding  to  similar  ones  found  in  other  parts  of  the 
district.  The  lower  zone  is  the  Glycymeris  zone  already  mentioned. 
About  800  feet  above  the  base  of  the  formation,  roughly  speaking, 
comes  a zone  characterized  by  an  abundance  of  Mulinia  (large), 
Area,  sand  dollars  (Echinarachnius) , etc.,  which  may  be  referred  to 
here  and  in  the  Kettleman  Hills  as  the  upper  Mulinia  zone,  as  it  is 
the  uppermost  bed  in  which  large  specimens  of  this  genus  are  found. 
This  zone  is  usually  coincident  with  the  upper  portion  of  the  blue- 
sand  zone.  The  third  main  zone  may  be  called  the  Pecten  coalinga- 
ensis  zone,  owing  to  the  nonoccurrence  of  this  species  at  other  hori- 
zons. It  is  within  300  to  400  feet  below  the  top  of  the  formation  and 
contains  a well-preserved  and  extremely  varied  fauna,  including 
Pecten  coalingaensis  and  Pecten  wattsi  as  about  the  most  typical 
forms,  together  with  many  sand  dollars,  sea  urchins,  brachiopods, 
etc.  The  fourth  zone  includes  the  summit  beds  of  the  formation, 
which  contain  Mya,  Ostrea,  etc.,  and  which  are  called  the  upper  Mya 
zone.  These  four  zones  do  not  include  all  the  important  fossil  beds 


GEOLOGY. 


51 


in  the  formation,  but  are  those  that  have  been  found  most  persistent 
and  easily  recognizable  and  therefore  most  valuable  as  datum  lines. 

The  following  columnar  sections  of  the  formation  in  different  parts 
of  the  Kreyenhagen  Hills  give  a tabulated  description  of  the  forma- 
tion as  it  occurs  typically  and  convey  an  idea  of  the  variability  of 
the  beds: 

Section  of  Etchegoin  formation  on  Zapato  Creek. 

Feet. 

Light-gray  and  olive-gray  sandy  clay  and  sand,  with  sandstone  layers  at  top 
containing  Mya,  Ostrea,  Area,  Neverita , etc. ; the  upper  Mya  zone;  overlain  by 

gravel  of  Paso  Robles  formation 300 

Olive-gray  fine  sand  and  pebbly  sand,  with  thin  sandstone  layers.  Rich  fossil 
zone  at  top  containing  Pecten  wattsi,  P.  coaling aensis,  brachiopods,  sea  urchins, 

etc.;  the  Pecten  coalingaensis  zone 400 

Bed  of  light-blue  sand,  the  highest  of  the  blue-sand  zone 10 

Massive  beds  of  gray  sand  and  sandy  clay  with  occasional  thick  beds  of  blue 

sand ; a bed  containing  Area  in  quantities  at  the  base 200 

Similar  gray  and  blue  beds  with  a 20-foot  zone  at  base  composed  of  massive, 
olive-gray,  compact  sand  containing  many  inconstant  laminae  of  hard  brown- 
ish-gray sandstone 850 

Gray  sand "350 

Prominent  bed  of  cavernous- weathering  blue  sand 50 

Alternating  thick  beds  of  gray  sands  and  bluish  clay,  with  thin  layers  of  sandy 
clay,  and  with  three  prominent  beds  of  blue  sand  in  the  lower  100  feet.  This 

basal  portion  is  probably  the  upper  Mulinia  zone 250 

Olive  and  light-gray  sand  and  sandy  clay 500 

Prominent  beds  of  blue  sand  at  top  and  base,  with  prominent  massive  beds  of 
olive-gray  medium-grained  and  pebbly  sand  and  minor  beds  of  clay  and  blue 
sand  between;  this  is  the  base  of  the  blue-sand  zone  and  approximately  that 
of  the  Etchegoin 475 

3,  475 

Section  of  Etchegoin  formation  on  Canoas  Creek. 

Fine  gray  sand  and  clay  with  occasional  hard  layers;  zone  of  Mya,  etc.;  over- 

lain  by  gravel  of  Paso  Robles  formation 450 

Gray  sand  and  clay  in  alternating  beds  of  variable  thickness 1,  700 

Top  of  blue-sand  zone;  massive  gray  sand  both  coarse  and  fine,  interbedded 
with  clay  in  lesser  amounts  and  occasional  heavy  beds  of  blue  sand;  contains 
numerous  sand  dollars  and  a zone  at  the  base  with  Mulinia,  Cardium,  Glycy- 

meris,  Mytiloconcha,  etc.;  the  upper  Mulinia  zone 550 

Similar  beds  to  the  base  of  the  zone  of  blue  sand.  Beds  at  base  containing  sand 
dollars  ( Echinarachnius ) Solen,  Cardium,  Nassa,  etc 900 

3,  600 

Section  of  Etchegoin  formation  3\  miles  southeast  of  Big  Mar  Canyon. 

Thinly  bedded  hard  white  porcelaneous  shale,  with  whitish-gray  fine  sand, 
pebbly  sand,  and  sandy  clay,  containing  lenticular  layers  and  nodules  of  por- 
celaneous shale  and  many  bone  fragments 250 

Alternating  thick  zones  of  whitish-gray  sand  and  clay 1,  080 

Solid  zone  of  thin-bedded  pebbly  sandstone 45 

Whitish-gray  sand  and  clay  with  a 15-foot  bed  of  coarse  pebbly  sand  in  middle. . 660 


52 


COALING  A OIL  DISTRICT,  CALIFORNIA. 


Feet. 


Prominent  beds  of  compact  gray  sand  with  softer  sand  and  sandy  clay  between; 

whitish  gray  sand  with  black  pebbles  at  base 210 

Compact  fine  gray  sand  streaked  with  layers  of  fine  whitish  sand  and  sandy  clay.  420 
Compact,  slightly  gritty  white  shale  somewhat  similar  to  the  Santa  Margarita. . . 10 

Solid  zone  of  gray  sandstone,  coarse  pebbly  sandstone,  and  hard  calcareous 

shale 40 

Fine  gray  sand 50 

Highest  bed  of  blue  sand,  with  a 10-foot  layer  of  pebbles  at  base  and  a 3-foot 
layer  full  of  sand  dollars,  barnacles,  areas,  etc.,  20  feet  above  base;  probably 

upper  Mulinia  zone 80 

Interbedded  blue  sand  and  sandy  clay  with  a prominent  20-foot  bed  of  blue 
sand  at  base;  probably  the  zone  of  Crepidula,  Solen,  etc.,  found  1 mile  to  the 

northwest 120 

Minor  beds  of  blue  sand,  with  a thick  zone  of  hard  calcareous  shale  in  middle. . 90 

Prominent  blue-sand  bed,  pebbly  toward  the  base  and  containing  many  sand 

dollars ! 90 

Soft  gray  sand 70 

Very  prominent  blue  sand 40 

A prominent  30-foot  bed  of  blue  sand  at  base  overlain  by  bluish  and  gray  sand 
and  three  less  prominent  beds  of  blue  sand 250 


3,  500 

McLure  Valley. — The  Etehegoin  probably  outcrops  over  a small 
area  in  the  Avenal  syncline  in  McLure  Valley  above  the  Jacalitos  for- 
mation, and  is  characterized  at  its  base  by  blue  sands,  but  it  can  not 
be  definitely  recognized.  The  thickness  of  beds  above  the  Santa 
Margarita  in  this  region  is  so  great  that  some  Etehegoin  must  be  pres- 
ent in  addition  to  the  Jacalitos.  No  fossils  have  been  found,  and 
there  is  no  direct  evidence  on  which  to  base  a separation  between  the 
two  formations,  so  that  the  line  of  contact  mapped  is  arbitrary.  The 
highest  beds  appearing  in  the  syncline,  which  are  taken  to  be  the  basal 
beds  of  the  Etehegoin,  consist  of  blue  sands.  Above  these  every- 
thing is  covered  by  the  recent  alluvial  deposits  of  the  valley. 

Kettleman  Hills. — The  Etehegoin  is  excellently  exposed  in  the  Ket- 
tleman  Hills,  where  it  is  a thick  formation  similar  in  character  to  the 
same  terrane  in  other  parts  of  the  district.  Its  lower  portion  appears 
along  the  axis  of  the  Coalinga  anticline,  but  although  the  lowest  beds 
that  the  plunging  anticline  brings  to  the  surface  are  very  nearly  the 
basal  beds  of  the  formation  no  underlying  formation  is  known  to  be 
exposed.  The  uppermost  beds  appear  all  around  the  Kettleman  Hills 
and  are  everywhere  overlain,  with  apparent  conformity,  by  the  fresh- 
water beds  at  the  base  of  the  Paso  Robles.  The  greatest  thickness 
that  has  been  found  exposed  is  in  the  south-central  part  of  the  hills, 
on  the  southwestern  flank  of  the  anticline,  where  the  beds  below  the 
fresh-water  horizon  measure  over  3,000  feet. 

Different  horizons  in  the  Etehegoin  of  the  Kettleman  Hills  afford 
good  datum  lines  that  may  be  recognized  by  means  of  the  character- 
istic faunas  and  the  constancy  of  the  beds  containing  them,  and  it  is 


GEOLOGY. 


53 


convenient  to  designate  these  briefly,  beginning  with  the  summit  of 
the  formation  as  a constant  datum  line  and  going  down.  The  summit 
of  the  formation  is  marked,  as  it  is  in  portions  of  the  Kreyenhagen 
Hills,  by  a constant  fossiliferous  zone  of  sand  and  sandstone  inter- 
bedded  with  dark  clay,  which  here,  as  in  the  Kreyenhagen  Hills,  may 
be  called  the  upper  Mya  zone,  because  of  the  great  abundance  of 
fossils  of  the  genus  Mya.  It  is  also  full  of  other  fossils,  small  yellow 
Littorina  and  small  oysters  being  especially  common.  This  zone  has 
a thickness  varying  between  200  and  300  feet,  and  is  prominent  in  the 
topography  because  it  usually  forms  a line  of  hills.  In  the  southern 
part  of  Kettleman  Hills  it  forms  the  main  ridge.  Below  it  comes  a 
zone  of  uneven  thickness,  usually  measuring  about  700  feet,  which  in 
some  portions  of  the  hills  is  composed  almost  entirely  of  fine  inky- 
blue  clay,  and  in  others  of  clay  and  sand  interbedded  in  varying  pro- 
portions. Toward  the  base  of  this  zone,  usually  between  700  and  900 
feet  below  the  top  of  the  formation,  there  is  a zone  of  fossiliferous 
sandstone  beds  equivalent  to  the  zone  of  Pecten  coalingaensis  occur- 
ring in  the  Kreyenhagen  Hills.  The  beds  at  this  horizon  likewise 
show  a tendency  to  form  hills  or  knobs,  but  these  are  not  so  promi- 
nent as  those  of  the  upper  Mya  zone. 

Below  this  the  formation  is  largely  sand  and  clay,  chiefly  sand, 
down  to  the  base,  the  lower  portion  here,  as  elsewhere,  being  com- 
posed of  beds  of  ordinaiy  sand  alternating  with  beds  of  blue  sand. 
The  next  prominent  fossil  bed  contains  Mya  in  large  quantities,  and 
will  be  referred  to  as  the  lower  Mya  bed.  It  occurs  between  very 
prominent  beds  of  blue  sand  on  the  summits  of  hills ; and  in  the  north- 
central  portion,  of  the  Kettleman  Hills  forms  the  main  ridge.  Owing 
to  the  fact  that  the  formation  is  thicker  in  the  southern  than  in  the 
northern  portion  of  the  hills  and  apparently  thicker  on  the  western 
than  on  the  eastern  flank  of  the  anticline,  the  distance  below  the  sum- 
mit of  the  formation  at  which  this  and' other  beds  occur  can  not  be 
stafed  as  a constant.  The  variation  of  this  zone  is  between  about 
1,900  and  2,400  feet  below  the  summit.  One  of  the  fossils  most  in 
evidence  in  the  Kettleman  Hills  is  the  large  Mulinia;  a bed  contain- 
ing abundant  specimens  of  this  species  occurs  about  100  feet  below 
the  lower  Mya  bed.  It  is  the  highest  horizon  at  which  the  large 
specimens  have  been  found,  and  is  with  little  doubt  the  upper  Mulinia 
zone  of  Kreyenhagen  Hills.  In  the  northern  portion  of  Kettleman 
Hills  it  is  near  the  base  of  the  exposed  series,  and  is  the  lowermost 
easily  recognizable  zone;  in  the  central  portion  of  the  hills  it  still 
persists,  but  lies  above  exposed  beds  of  considerable  thickness. 
Another  zone  in  which  Mulinia  occurs  very  abundantly  in  Kettleman 
Hills  is  between  500  and  700  feet  below  the  upper  one,  and  may  be 
referred  to  as  the  Glycymeris  bed,  for  the  reason  that  it  contains  an 
association  of  fossils,  including  Mytiloconcha,  Glycymeris , etc.,  similar 


54 


COALTNGA  OTL  DISTRICT,  CALIFORNIA. 


to  the  bed  so  named  north  of  Coalinga.  It  is  about  the  lowest  bed 
exposed,  and  is  approximately  at  the  base  of  the  Etcliegoin  formation. 

The  following  sections  represent  fairly  well  the  lithologic  character 
and  variations  of  the  Etchegoin  in  the  Kettleman  Hills.  Variability 
is  the  rule,  and  it  would  be  difficult  to  find  any  two  sections  in  which 
the  same  beds  are  exposed  and  the  characteristics  are  constant: 


Section  of  Etchegoin  formation  on  southwest  flank  of  Kettleman  Hills , along  road  6 miles 

from  northwest  end  of  hills. 


Foot. 


Yellowish-gray  sancl  and  clay,  with  some  dark  clay;  many  fragments  of  porce- 
lain shale  on  surface;  small  oysters  in  sand  at  top,  and  yellow  calcareous  shale 

lenses  in  bluish-black  clay  at  base;  tipper  My  a zone. . 125 

Alternating  beds  of  fine  drab  gypsiferous  sand,  sandy  clay,  and  drab  to  bluish 
clay,  with  occasional  sandstone  layers,  and  with  a bed  at  the  base  containing 

delicate  fossils,  Nucula , etc 250 

Similar  beds,  with  layers  of  iron-stained  sandstone  at  base 115 

Similar  gypsiferous  beds,  with  light-colored  sand  predominating;  the  Pecten 

coaling aensis  zone  should  be  here  somewhere,  but  was  not  found 250 

Inky-blue  clay  with  minor  beds  of  sand  and  with  a hard  1-foot  bed  of  yellow 

limestone  in  middle 290 

Fine  sand  and  some  light  and  dark  clay,  with  hard,  very  gypsiferous,  yellow 
and  variegated  sandstone  at  the  top,  and  interspersed  hard  layers  below; 

sandstone  with  Solen,  etc.,  near  base 135 

Highest  blue-sand  bed 45 

Grayish-blue  massive  sand  and  pebbly  sand,  with  fossils 130 

Thinly  and  massively  bedded  drab  and  light-gray  sand  with  occasional  beds  of 
blue  sand  and  layers  of  inky-blue  clay,  white  clay,  and  pebbles;  the  sand  at 

base  is  the  lower  My  a bed : 550 

Massive  beds  of  blue  and  gray  sand,  with  Mulinia , etc.,  at  base;  upper  Mulinia 

zone 100 

Less  prominent  beds  of  blue  and  gray  sand  with  sand  dollars,  oysters,  etc 300 


2,  300 


On  the  northeastern  flank  of  the  anticline  in  this  same  portion  of 
the  hills  the  beds  are  repeated  with  approximately  the  same  thick- 
ness, but  the  section  measured  made  it  appear  that  there  was  possibly 
a slight  thinning  on  that  side. 

The  next  section  is  on  the  southwestern  flank  of  the  anticline  in  the 
south-central  portion  of  the  hills,  beginning  at  the  1,030-foot  hill  on 
the  main  ridge  in  the  center  of  sec.  3,  T.  23  S.,  R.  18  E.,  and  extend- 
ing northeastward  across  the  strike  of  the  beds  to  the  anticlinal  axis. 


Section  of  Etchegoin  formation  on  southwest  flank  of  Coalinga  anticline  in  central  portion 

of  Kettleman  Hills. 


Feet. 


Inky-blue  clay  below  fresh-water  bed 50 

Yellow  and  gray  sand,  full  of  fragments  or  nodules  of  porcelain  shale  and  of  fos- 
sils, Mya,  Macoma,  Solen , Ostrea,  Area,  Littorina,  etc.;  the  upper  Mya  beds. . 200 

Inky-blue  clay  zone;  sandy  beds  at  top  containing  innumerable  small  oysters; 
occasional  layers  of  yellow  calcareous  shale;  a thin  bed,  15  feet  above  base, 
of  coarse  purple  and  yellow,  iron-stained,  and  exceedingly  gypsiferous  sand- 
stone with  many  fossils,  probably  the  Pecten  coalingaensis  zone 725 


GEOLOGY. 


55 


Feet. 

Mostly  light-gray  and  drab  sand,  with  beds  of  dark  clay  in  minor  amount;  a 
pebbly  sand  layer  200  feet  below  top ; pebbly  sand  and  iron-hardened  sand- 
stone layers  near  base 1,  400 

Blue-sand  zone,  several  massive  beds  of  blue  sand  and  pebbly  sand  interbedded 
with  fine  light-gray  and  drab  sand,  sandy  shale,  and  pebbly  sand  and  occa- 
sional iron-hardened  beds;  at  top  is  probably  the  upper  Mulinia  zone;  the 
basal  sand  is  full  of  fossils,  Mulinia , Mytiloconcha,  Glyqjmeris , etc.,  and  is  the 
lower  Mulinia  zone 675 

3.  050 

As  may  be  inferred  from  an  examination  of  these  two  sections,  the 
anticline  plunges  from  the  locality  of  the  second  toward  that  of  the 
first,  and  a much  greater  thickness  of  beds  is  exposed  in  the  second. 
The  upper  Mulinia  zone  occurs  2,000  feet  below  the  summit  in  the 
first,  whereas  the  bed  that  has  been  correlated  with  it  in  the  second 
occurs  over  300  feet  lower.  It  seems  probablp  from  this  and  similar 
instances  in  other  sections  that  the  formation  thickens  toward  the 
south  between  the  top  and  this  bed,  the  thickening  being  similar  to 
that  which  takes  place  between  the  oil  field  north  of  Coalinga  and 
Kreyenhagen  hills.  It  may  reasonably  be  assumed  that  a thickening 
takes  place  also  below  the  upper  Mulinia  zone,  and  that  the  base  of 
the  formation  is  not  so  far  below  this  zone  in  the  northern  portion  of 
the  hills  as  farther  south. 

Toward  the  northern  end  of  the  hills,  as  shown  by  the  map,  the 
Etchegoin  plunges  completely  beneath  the  Paso  Robles  formation 
and  does  not  appear  again  until  brought  up  by  the  oppositely  plung- 
ing anticline  on  Anticline  Ridge.  Toward  the  southern  end  of  the 
hills  the  formation  becomes  covered  more  and  more  by  surface  sand 
and  soil,  and  both  its  zones  and  structure  are  obscured.  At  the 
southern  end  of  the  hills  it  does  not  pass  below  the  Paso  Robles,  but 
exposes  beds  not  far  above  the  base. 

Importance  with  relation  to  oil. — Nowhere  within  the  Coalinga  dis- 
trict is  the  Etchegoin  formation  known  to  contain  any  petroleum, 
but,  like  the  Jacalitos,  it  has  an  important  relation  to  the  question  of 
accessibility  of  the  oil.  Some  wells  in  the  Coalinga  field  pass  through 
a considerable  portion  or  the  whole  of  this  formation  before  reaching 
the  Jacalitos  or  lower  formations.  All  wells  drilled  around  the  edge 
of  Pleasant  Valley,  or  on  Anticline  Ridge,  or  in  the  Kettleman  Hills, 
wall  have  to  pass  through  this  formation,  and  its  thickness  must  be 
taken  into  account  in  calculating  the  depth  of  the  oil  sands.  The 
great  increase  in  thickness  that  takes  place  in  this  and  the  other 
post-Eocene  formations  south  of  Waltham  Creek  has  an  all-important 
bearing  on  such  calculations. 


56  COALINGA  OIL  DISTRICT,  CALIFORNIA. 

PASO  ROBLES  FORMATION  (PLIOCENE-LOWER  PLEISTOCENE). 

Definition  and  general  description. — The  Etchegoin  is  overlain  along 
the  border  of  the  valley  by  a thick  terrane  of  beds  of  gravel,  sand, 
clay,  sandstone,  conglomerate,  and  some  limestone  that  forms  the 
uppermost  member  of  the  series  of  upturned  formations  exposed  in 
the  monocline  on  the  eastern  flank  of  the  Diablo  Range.  It  differs 
materially  from  the  formations  so  far  described  in  that  its  origin  is 
doubtful,  being  in  part  fresh  water,  in  part  marine,  and  in  large  part 
probably  of  subserial  origin.  In  the  Kettleman  Hills,  where  these 
beds  are  best  exposed,  the  basal  sand,  which  appears  to  lie  conform- 
ably upon  the  marine  bed  at  the  top  of  the  Etchegoin,  contains  many 
fresh-water  fossils.  The  beds  above  this  have  a thickness  of  several 
thousand  feet,  and  as  far  as  observed  are  unfossiliferous  except  at 
one  horizon  near  the  summit  at  which  a few  marine  fossils  have  been 
found.  Along  the  foothills  of  the  Diablo  Range  in  the  Coalinga  dis- 
trict the  basal  fresh- water  beds  have  not  been  recognized  and  may 
be  lacking.  Gravel  and  sand  beds  belonging  to  the  same  series  over- 
lie  the  Etchegoin  with  local  appearances  of  unconformity. 

This  whole  series  of  tilted  beds  overlying  the  Etchegoin  is  referred 
to  here  and  mapped  as  one  formation,  the  Paso  Robles,  for  the  reason 
that  it  appears  to  be  a continuous  succession  and  can  not  be  con- 
sistently subdivided  in  different  regions.  It  was  formed  without 
doubt  under  varying  conditions  of  deposition,  but  it  may  or  may  not 
represent  a continuous  period.  It  began  to  be  formed  in  some  por- 
tion (probably  the  earlier  portion)  of  the  Pliocene  epoch,  and  prob- 
ably represents  a continuation  of  deposition  well  into  the  Pleistocene. 
Its  summit  may  be  considered  as  the  highest  bed  markedly  affected 
by  the  great  uplift  that  took  place  early  in  Pleistocene  time  through- 
out the  Coast  Range  region,  and  as  unconformably  overlain  by  the 
more  recent  horizontal  terrace  deposits  and  alluvium. 

The  highest  portion  of  the  formation  exposed  appears  near  the  edge 
of  Kettleman  Plain  in  the  south-central  part  of  the  Kettleman  Hills, 
but  the  summit  of  the  formation  as  above  defined  is  not  exposed.  It 
is  probable  that  the  edge  of  the  hills  there  marks  the  approximate 
summit  of  the  tilted  beds.  The  formation  may  be  recognized  most 
easily  by  the  fresh-water  fossils  and  strange  bone  beds  at  its  base,  by 
its  position  overlying  all  the  other  formations  and  bordering  the  valley  j 
and  by  the  prevalence  in  it  of  prominent  beds  of  bowlder  gravel,  which 
is  much  coarser  and  more  abundant  than  in  any  of  the  other  Tertiary 
formations.  Otherwise  this  formation  resembles  some  of  the  others 
closely,  and  it  is  frequently  difficult  to  differentiate  them. 

This  formation  is  called  Paso  Robles,  because  it  is  the  same  as  the 
formation  which  spreads  over  the  summit  of  the  Temblor  Range 
south  of  Polonio  Pass,  the  divide  between  the  Antelope  and  Cholame 


GEOLOGY. 


57 


valleys,  and  from  there  southward  to  the  Palo  Prieto  Pass,  and  which 
may  be  traced  thence  to  Paso  Robles  in  the  Salinas  Valley,  where  it 
was  named  by  H.  W.  Fairbanks.0 

The  formation  in  the  type  locality  consists  of  a thickness  of  at  least 
1,000  feet  of  slightly  coherent  conglomerate,  gravel,  sand,  and  clay 
in  stratified  deposits  that  have  been  locally  tilted  to  moderate  angles 
and  that  lie  unconformably  upon  the  marine  Pliocene  and  older  forma- 
tions. The  formation  is  unfossiliferous  and  is  believed  by  Fairbanks 
to  be  of  fresh-water  origin. 

Kettleman  Hills. — The  Paso  Robles  is  completely  exposed  only  in 
the  Kettleman  Ilills,  and  its  occurrence  there  forms  the  basis  for 
most  of  the  discussion  given  here.  As  shown  on  the  map  it  occu- 
pies an  almost  complete  fringe  around  the  hills,  dipping  steeply  away 
on  the  flanks  of  the  anticline  which  exposes  the  Etchegoin  beneath. 
Throughout  the  Kettleman  Hills  the  Etchegoin  and  Paso  Robles  are 
apparently  conformable,  and  in  places,  especially  toward  the  north- 
ern end  of  the  hills,  there  are  indications  that  a gradual  change  took 
place  toward  the  end  of  the  deposition  of  the  former,  that  shallow- 
water  marine  conditions  gave  way  to  brackish-water  and  this  in  turn 
to  fresh-water  conditions.  The  upper  Mya  beds  are  constant  at  the 
top  of  the  Etchegoin  and  contain  a fauna  that  with  the  possible  excep- 
tion of  one  species,  Littorina,  is  indicative  of  estuarine  conditions. 
And  these  beds,  in  some  places  at  least,  grade  into  the  fresh-water 
beds  above. 

The  thickness  of  the  basal  fossiliferous  zone  of  the  Paso  Robles  is 
usually  no  ‘more  than  60  to  100  feet,  although  it  is  as  much  as  300 
feet  on  the  southeastern  side  of  the  Kettleman  Hills  a few  miles  north- 
east of  Avenal  Gap.  The  beds  consist  principally  of  fine-grained 
earthy  sand,  very  gypsiferous,  and  frequently  containing  many  scat- 
tered pebbles.  The  fossils  are  entirely  fresh-water  forms  and  occur 
in  places  very  thickly  embedded.  Along  a part  of  the  northeastern 
side  of  the  hills  certain  layers  are  so  indurated  as  to  form  hard  lime- 
stone and  to  produce  a ridge  marking  the  contact  between  the  Etch- 
egoin and  the  Paso  Robles  formations.  Associated  with  the  fresh- 
water beds  are  abundant  small  bones  that  have  not  been  identified. 
They  are  characteristic  of  this  zone,  but  have  been  found  also  in 
association  with  marine  fossils  in  a bed  many  hundred  feet  below  the 
top  of  the  Etchegoin.  The  only  fossils  found  in  the  Paso  Robles  at 
a higher  horizon  than  the  basal  zone  are  noted  in  the  second  tabular 
section  below  (p.  59).  A few  good  specimens  of  these  and  many 
fragments  were  found  in  two  beds  of  coarse  pebbly  sand  15  feet  apart 
in  the  upper  portion  of  the  formation. 

Above  the  basal  zone  the  formation  consists  of  a continuous  unvaried 
succession  of  alternating  zones  and  beds  of  unconsolidated  light-gray 


Geologic  Atlas  U.  S.,  San  Luis  folio  (No.  101),  U.  S.  Geol.  Survey,  1904. 


58 


COALINGA  OIL  DISTBICT,  CALIFOBNIA. 


and  yellowish  fine  sand,  sandy  clay,  light  and  dark  clay,  coarse  darker 
gray  sand,  and  gravel  and  bowlder  beds,  and  occasionally  interbedded 
layers  of  hard  sandstone.  The  whole  series  is  gypsiferous.  The  beds 
are  usually  fairly  thick  and  massive  and  the  bedding  planes  not  very 
pronounced,  although  in  some  places  the  strata  are  sharp  and  square 
cut.  Frequently  the  stratification  and  the  dip  appear  more  distinct 
from  a distance  than  from  near  at  hand.  Many  of  the  coarse  sand 
and  gravel  deposits  are  roughly  stratified  and  exhibit  lenticular  struc- 
ture, grading  within  a short  distance  into  finer  deposits.  In  general, 
the  formation  resembles  very  closely  the  recent  alluvial  deposits  and 
is  almost  indistinguishable  from  them  except  by  means  of  the  disturbed 
position  of  its  beds. 

A marked  feature  of  the  gravel  is  the  predominance  in  it  of  sub- 
angular  fragments  of  hard  white  siliceous  shale,  derived  presumably 
from  the  shale  either  of  the  Tejon  or  of  the  Santa  Margarita.  This 
shale  is  very  resistant  and  lends  itself  remarkably  to  preservation  in 
younger  deposits  of  gravel  and  debris.  The  other  pebbles  and  bowl- 
ders in  the  gravel  beds  of  the  Paso  Robles  are  of  many  different  Coast 
Range  types  of  rock  and  have  probably  been  derived  chiefly  from 
the  Diablo  Range.  Many  of  them  are  angular  and  have  been  sub- 
jected to  little  wear  before  being  deposited.  Rocks  of  a granitic  type 
are  very  common,  and  the  area  also  contains  serpentine,  porphyries 
of  different  kinds,  different  varieties  of  basic  igneous  rocks,  both  fresh 
and  considerably  altered,  jasper,  sandstone,  conglomerate,  quartz, 
schist,  etc. 

The  lower  beds  of  the  Paso  Robles  in  the  Kettleman  Hills  are  as  a 
rule  not  of  very  coarse  material,  although  pebbles  are  scattered 
through  them.  The  first  important  zone  of  coarse  gravel  appears 
several  hundred  feet  above  the  base.  It  is  associated  with  several 
beds  of  hard  sandstone,  and  in  consequence  shows  a marked  influence 
on  the  topography,  forming  a hill  on  each  of  the  lateral  ridges  descend- 
ing from  the  summit  to  the  valley.  This  zone  probably  occurs  at  a 
slightly  variable  horizon,  ranging  from  about  500  to  800  feet  above 
the  base  of  the  formation.  It  is  in  general  higher  toward  the  south 
in  the  hills,  and  may  thus  indicate  a thickening  of  the  formation  in 
that  direction.  Above  this  zone  occur  various  other  prominent  gravel 
zones. 

The  following  columnar  sections  represent  fairly  well  the  character 
of  the  formation  in  that  part  of  the  Coalinga  district  in  which  it  is 
most  completely  exposed.  In  each  place  the  section  was  started  at 
the  edge  of  Kettleman  Hills,  but  beds  were  not  found  exposed  for 
about  700  feet  into  the  hills  away  from  the  edge.  In  this  border 
area  the  beds  almost  certainly  have  a fairly  steep  dip,  and  it  would  be 
conservative  to  add  at  least  150  feet  to  the  total  thickness  given  to 
represent  the  summit  beds  there. 


GEOLOGY. 


59 


The  first,  section  was  made  on  the  southwest  side  of  the  hills,  about 
9 miles  northwest  of  Avenal  Gap,  and  is  as  follows: 

Section  of  Paso  Robles  formation  9 miles  northwest  of  Avenal  Gap. 

Feet. 


Mostly  fine,  earthy,  drab  and  yellowish-gray,  faintly  bedded  massive  sand, 
with  occasional  roughly  aggregated  beds  and  lenses  of  pebbles  and  bowlders; 

the  stratification  bedding  is  very  apparent  from  a distance 500 

Similar  beds  of  hard  and  compact  straw-colored  massive  sandy  clay  , with  part- 
ings of  gypsiferous  sandstone 300 

Similar  clay  interbedded  with  pure  sand,  gravelly  sand,  and  sandstone  layers, 

with  a hard  sandstone  bed  at  base 75 

Compact,  drab,  gray,  and  straw-colored  coarse  and  fine  sand 200 

Thin  layers  of  gravel  and  coarse  sands,  with  a bowlder  bed  several  feet  thick  at 

base 75 

Pure  fine  sand  similar  to  that  .above,  with  hard  sandstone  layers 125 

Mostly  gravel,  composed  in  large  part  of  fragments  of  hard  , white,  siliceous  shale, 
interbedded  with  sand  and  sandy  clay,  and  with  hard  sandstone  beds  at  top 

and  base 75 

Alternating  beds,  from  a few  inches  to  1 or  2 feet  thick,  of  loose  and  compact 
fine  sand,  roughly  bedded  slightly  gritty  clay,  pebbly  sand,  gravel,  and  hard 
usually  purplish  sandstone;  some  of  the  sand  is  speckled  all  over  with  inclu- 
sions of  hard,  white  siliceous  shale,  and  the  gravel  is  largely  composed  of  it . . 225 

Pure  clay  and  sandy  clay . 75 

Fine  clay  and  sand  at  tap,  grading  down  to  coarse  sand  and  pebble  and  bowlder 
beds  at  base;  some  finedrabsand  forms  hard,  massive,  roughly  laminated  beds.  75 

Drab  sand  with  some  pebbles  and  with  gravel  and  hard  sandstone  beds  at  base. . 150 

Sand  and  clay  and  a few  hard  sandstone  beds 375 

Gravelly  sand 100 

Loose  earthy  sand  full  of  pebbles,  bowlders,  and  fragments  of  white  siliceous 
shale,  and  containing  fresh- water  shells,  and  bones;  at  the  base  is  a sharp 
change  to  the  dark  clay  and  upper  My  a beds  of  the  Etchegoin 50 


2, 400 

The  following  section  was  made  on  the  southwestern  flank  of  the 
Kettleman  Hills,  along  the  Dudley-Lemoore  road,  which  crosses  about 
4 miles  northwest  of  Avenal  Gap : 

Section  of  Paso  Robles  formation  along  Dudley-Lemoore  road. 

Feet. 

Massive  1-  to  3-foot  beds  of  well-compacted  but  not  indurated  fine  sand,  clayey 
sand,  clay,  coarse  sand,  and  gravelly  sand,  with  several  beds,  many  feet  thick, 
of  coarse  gravels  and  bowlders  in  the  middle  and  at  the  base.  Much  gypsum 
occurs  in  fine  particles  and  as  a filling  in  cracks,  causing  hardening  in  indi- 
vidual beds  and  in  spots.  Some  sand  and  gravel  beds  are  lenticular.  One 
hundred  feet  below  top  are  two  coarse  sand  beds,  15  feet  apart,  containing 


Ostrea  and  Littorina,  marine  fossils 400 

Yellowish-gray  earthy  sand,  sandy  clay,  and  clay  in  well-defined  massive  beds 

with  some  pebbly  sand 650 

Dark  clay 75 

Thick  zone  of  pebbly  sand 150 

Chiefly  dark  clay _ 150 

Yellowish-gray  fine  sand  yielding  whitish  surface  sand 75 

Pebbly  sand .. 70 


60  COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Feet. 

Sandy  clay 80 

Chiefly  fine  gray  sand,  alternating  with  pebbly  sand,  sandy  clay,  and  clay;  a 

thick  zone  of  pebbles  and  bowlders  occurs  about  350  feet  below  the  top 1, 100 

Chiefly  fine  gypsiferous  ashlike  light-gray  sand,  with  dark  clay  layers  and  many 
large  pebbles  scattered  through,  but  no  prominent  gravel  beds;  lower  portion 
is  the  fossiliferous  fresh- water  zone,  but  no  fossils  were  here  found;  it  overlies 
dark  clay  and  My  a beds  at  the  top  of  the  Etchegoin 350 


3, 100 

Kreyenhagen  and  Jacalitos  hills. — The  Paso  Robles  beds  clip  under 
the  Kettleman  Plain  and  reappear  on  the  western  arm  of  the  syncline 
along  the  border  of  the  Kreyenhagen  and  Jacalitos  hills.  As  in  the 
Kettleman  Hills,  the  formation  dips  more  steeply  and  exposes  a much 
greater  thickness  toward  the  south,  but  here  this  difference  is  even 
more  pronounced.  The  beds  have  a dip  of  only  a few  degrees  north- 
west of  Zapato  Creek  and  form  a comparatively  narrow  belt  to  where 
they  are  finally  overlapped  by  the  alluvial  deposits  of  Pleasant  Valley. 
South  of  Canoas  Creek  the  Paso  Robles  beds  rise  to  extremely  steep 
dips,  appearing  almost  overturned  in  places,  and  cover  a wide  belt. 
They  are,  however,  very  poorly  exposed.  The  formation  here 
consists  of  deposits  similar  to  those  in  the  Kettleman  Hills,  but  the 
basal  fossiliferous  beds  have  not  been  found.  The  formation  is 
chiefly  characterized  bv  its  heavy  gravel  deposits,  which,  contrary 
to  the  rule  in  the  Kettleman  Hills,  in  places  rests  directly  upon  the 
Etchegoin,  forming  high  hills  fronting  the  valley.  This  occurrence 
of  heavy  bowlder  deposits  near  the  base  has  led  to  the  theory  that 
possibly  the  fresh-water  basal  zone  is  lacking  and  that  a higher 
portion  of  the  Paso  Robles  has  overlapped  upon  the  Etchegoin. 
Northwest  of  Zapato  Creek  a distinct  unconformity  between  the 
Paso  Robles  and  the  Etchegoin  is  shown  to  exist  by  the  fact  that  the 
gravel  beds  of  the  former  overlap  upon  the  Etchegoin  and  locally 
cover  up  some  of  the  higher  beds  of  that  formation.  Southeast  of 
Big  Tar  Canyon  the  basal  portion  of  the  Paso  Robles  is  sand  and  clay 
and  is  marked  by  a zone  of  white  nodular  shale  beds,  interbedded  with 
sand,  containing  the  strange  bones  mentioned  before  as  occurring  in 
the  fresh-water  beds  in  the  Kettleman  Hills.  The  Etchegoin  and 
Paso  Robles  appear  conformable  in  the  southern  part  of  the  Kreyen- 
hagen Hills.  The  latter  has  a thickness  of  at  least  2,000  feet  and 
probably  much  more. 

Guijarral  Hills. — In  the  northern  part  of  the  Coalinga  district  the 
Paso  Robles  is  doubtless  continuous  beneath  the  valley  floor  but  does 
not  appear  exposed  except  in  the  Guijarral  Hills,  which  are  entirely 
covered  by  deposits  of  coarse  gravel  of  this  formation,  the  name  of 
the  hills  being  derived  from  this  feature.  The  beds  are  almost  hori- 
zontal but  appear  to  dip  slightly  toward  Pleasant  Valley  and  Pol- 
vadero  Gap,  giving  the  surface  of  the  hills  the  appearance  of  a plane 


GEOLOGY. 


61 


inclined  in  those  directions.  The  beds  are  exposed  by  the  Coalinga 
anticline  and  probably  belong  in  the  lower  middle  portion  of  the 
formation.  They  may  be  traced  northward  on  the  east  flank  of 
Anticline  Ridge,  but  are  throughout  this  region  poorly  exposed.  The 
contact  with  the  underlying  Etchegoin  can  not  be  definitely  traced 
nor  the  relations  of  the  two  formations  determined. 

Importance  with  relation  to  petroleum. — The  Paso  Robles  formation 
does  not  come  in  contact  with  the  oil-bearing  formations  and  contains 
no  traces  of  oil.  Over  most  of  the  area  in  which  it  occurs  it  is  sep- 
arated by  so  great  a thickness  of  deposits  from  the  productive  zones 
that  its  mere  presence  is  usually  sufficient  to  indicate  the  inaccessi- 
bility of  the  oil.  Around  the  border  of  Pleasant  Valley  and  on 
Anticline  Ridge  and  the  Guijarral  Hills,  however,  productive  wells 
may  later  be  put  down  through  this  formation. 

TERRACE  DEPOSITS  AND  ALLUVIUM. 

The  later  Pleistocene  and  recent  periods  are  represented  by  a 
mantle  of  alluvium  and  terrace  deposits  covering  the  floor  of  the 
Great  Valley  and  the  large  side  valleys,  and  extending  over  the 
bottom  of  most  of  the  smaller  valleys  and  canyons  and  the  lower 
slopes  of  the  foothills.  The  larger  areas  of  these  deposits  are  shown 
on  the  map  (PI.  I,  in  pocket)  in  white.  In  the  large  valleys  it  is 
probable  that  these  deposits  have  a thickness  of  several  hundred 
feet,  as  the  late  period  has  been  largely  one  of  aggradation.  Else- 
where the  deposits  are  merely  superficial.  All  of  the  smaller  valleys 
show  evidences  of  several  terraces  along  their  sides,  these  being 
especially  evident  along  Zapato  Creek,  where  at  least  seven  terraces 
may  be  counted.  Many  of  these  terraces  are  covered  with  stream 
gravel  and  sand.  The  greater  portion  of  the  whole  region  under 
discussion  is  covered  by  surface  soil  and  residual  sand  derived  from 
the  soft  formations.  All  of  these  comparatively  recent  deposits  are 
similar  in  materials  and  appearance  to  the  underlying  formations  and 
are  not  easily  distinguishable  from  them.  They  have  the  effect  of 
obscuring  the  main  facts  of  the  geology  over  large  areas. 

IGNEOUS  ROCKS. 

The  only  igneous  rocks  occurring  within  the  Coalinga  district  are 
associated  with  the  Franciscan  formation.  The  Cretaceous,  Ter- 
tiary, and  Quaternary  formations  were  not  affected  by  igneous 
intrusions,  and  there  is  no  evidence  that  there  was  volcanic  activity 
in  this  or  the  adjacent  regions  during  these  periods.  The  serpentine 
that  has  already  been  mentioned  as  covering  such  a wide  region  in 
the  heart  of  the  Diablo  Range  originated  as  an  intrusion  of  basic 
igneous  rock  into  the  Franciscan  sedimentary  formation  before  the 
beginning  of  the  period  in  which  the  Knoxville  and  Chico  formations 


62 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


were  laid  down.  Many  different  varieties  of  it  occur,  varying  from 
hard,  little-altered  peridotite,  in  which  the  constituent  crystals  are 
well  displayed,  to  much-metamorphosed  and  surficially  altered  ser- 
pentine and  related  minerals. 

Toward  the  head  of  White  Creek  a hill  formed  of  a hard  horn- 
blende-bearing igneous  rock  seems  to  have  been  intrusive  into  the 
serpentine.  It  is  a soda-bearing  syenite,  of  a variety  heretofore 
undescribed,  and  varies  from  an  extremely  fine-grained  to  a por- 
phyritic  facies  in  which  there  are  large,  perfect  crystals  of  horn- 
blende. The  area  of  this  rock  as  shown  on  the  map  is  slightly 
exaggerated  in  size. 

STRUCTURE. 

Some  of  the  broad  features  of  the  structure  of  the  Coalinga  district 
have  been  briefly  touched  on  in  the  preceding  discussions  of  the 
topography  and  geology.  The  structural  axes  and  the  general 
attitude  and  succession  of  the  strata  are  outlined  on  the  map  (PI.  II), 
and  therefore  merely  a general  review  of  the  whole  and  the  discussion 
of  certain  particular  points  is  necessary  here. 

CROSS  STRUCTURES  AND  THEIR  TOPOGRAPHIC  INFLUENCE. 

The  structure  of  the  Diablo  Range  is,  broadly  speaking,  anticlinal, 
and  its  eastern  flank  is  composed  of  a great  monocline  of  sedimentary 
strata  dipping  toward  the  San  Joaquin  Valley.  But  the  regularity 
of  this  monocline  is  broken  by  its  being  thrown  into  a series  of  waves 
and  offsets  by  various  important  as  well  as  minor  plunging  anticlinal 
and  synclinal  folds,  and  by  faults  that  run  in  various  directions  both 
parallel  with  and  oblique  to  the  main  structural  trend  of  the  moun- 
tains. This  main  trend  parallels  the  general  course  of  the  Sierra 
Nevada,  the  Coast  Ranges,  and  the  coast  in  this  portion  of  Cali- 
fornia, and  is  approximately  N.  35°  W.  to  N.  40°  W.  The  general 
orientation  of  the  secondary  structural  axes  is  considerably  more  to 
the  west  of  north  than  this.  These  show  their  influence  prominently 
in  the  topography  by  producing  the  oblique  spurs  and  valleys  dis- 
cussed under  the  subject  of  the  topography.  The  same  features, 
both  topographic  and  structural,  may  be  observed  south  of  the 
Coalinga  district  and  also  in  the  mountainous  tracts  west  of  it.  It 
is  due  to  such  structures  that  the  Gabilan  Range  converges  and 
joins  with  the  Diablo  Range  in  the  latitude  of  the  Coalinga  district; 
and  the  various  discontinuous  spurs  of  the  high  and  complex  portion 
of  the  Diablo  Range,  which  are  arranged  in  positions  en  echelon  with 
one  another,  may  be  explained  on  the  same  basis.  It  would  appear 
therefore  that  the  region  has  been  subjected  to  two  main  sets  of 
compressional  forces,  the  one  set  acting  on  a line  running  roughly 


GEOLOGY. 


63 


N.  50°  E.  and  the  other  set  being  along  a line  running  N.  20°  to  30°  E., 
making  a counter-clockwise  angle  toward  the  north  of  about  20°  to 
30°  with  the  former  set. 

PERIODS  OF  MOVEMENT  AND  THE  EFFECT  ON  FORMATIONS  OF  DIFFERENT 

AGES. 

A large  part,  if  not  the  major  part,  of  the  movement  that  has 
resulted  in  the  disturbance  of  the  Tertiary  beds  in  this  region,  and 
of  the  Cretaceous  beds  over  considerable  areas  in  which  they  were 
not  previously  greatly  disturbed,  took  place  in  Pleistocene  time- 
after  the  deposition  of  the  Paso  Robles  (Pliocene-Pleistocene)  forma- 
tion. This  feature  of  the  history  of  the  region  is  indicated  by  the 
fact  that  the  later  Tertiary  and  early  Pleistocene  formations  appear 
to  have  been  disturbed  almost  as  much  as  the  older  ones,  and  in 
some  places  as  much  as  the  Cretaceous  beds.  An  example  of  this  is 
found  in  the  beds  exposed  in  the  Coalinga  anticline,  which  dip  gently 
and  would  hardly  appear  to  have  been  folded  at  all  previous  to  the 
time  in  which  the  Etchegoin  (Pliocene)  beds  were  tilted  on  the  same 
anticline  to  the  vertical  position.  It  is  certain  that  important 
movements  were  taking  place  during  Cretaceous  and  Tertiary  time, 
notably  at  the  close  of  the  Tejon  (Eocene)  period  of  deposition,  when 
the  beds  of  that  age  were  uplifted  and  greatly  disturbed  before  the 
subsidence  that  allowed  the  deposition  of  the  Vaqueros  (lower 
Miocene)  beds  on  their  eroded  surface,  and  also  at  the  close  of  the 
Vaqueros  period.  The  fact  that  all  the  formations  from  the  Creta- 
ceous to  the  lower  Pleistocene  appear  in  places  to  be  conformable  in 
dip,  and  that  at  least  the  Miocene,  Pliocene,  and  later  deposits  almost 
invariably  appear  so,  indicates  that  the  whole  series  was  affected  as 
one  during  the  Pleistocene  by  extraordinarily  severe  disturbances. 

In  the  Tertiary  formations  the  land  movements  have  resulted 
chiefly  in  folding  rather  than  in  faulting.  The  strata  of  these  forma- 
tions are  everywhere  tilted  at  angles  ranging  from  a few  degrees  to 
the  vertical  and  are  locally  overturned,  but  evidences  of  faulting 
are  by  no  means  as  frequent.  The  older  formations,  on  the  other 
hand,  are  much  faulted  as  well  as  folded,  and  many  faults  occur  in 
them  that  have  not  been  mapped.  The  Knoxville-Chic o (Cretaceous) 
rocks  exposed  along  Los  Gatos  Creek  afford  an  excellent  example  of 
the  very  great  number  of  large  and  small  faults  occurring  along  a 
fault  zone  such  as  that  which  determines  the  position  of  this  old 
valley. 

It  has  been  pointed  out  in  the  description  of  the  formations  how 
they  vary  in  thickness  within  short  distances.  This  variability  is  a 
characteristic  feature  of  the  geology  of  the  region.  In  the  post- 
Eocene  formations  it  may  be  explained  on  the  theory  that  the  gradual 


64 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


subsidence  which  took  place  during  the  different  periods  progressed 
more  rapidly  toward  the  south  than  it  did  in  the  northern  part  of  the 
Coalinga  district,  where  the  shore  line  must  have  been  near,  and  that 
the  periods  of  land  conditions  interrupting  the  progress  of  sedimenta- 
tion were  more  prolonged  and  frequent  in  the  northern  region. 

The  number  of  mutually  unconformable  formations  present  in  the 
Coalinga  district  proves  that  the  region  was  undergoing  almost  con- 
tinuous movements.  The  unconformities  are  rarely  very  apparent 
at  the  contact  between  the  formations,  and  the  fact  of  the  existence 
of  unconformable  relations  is  usually  to  be  made  out  only  from  a 
detailed  study  (1)  of  the  areal  distribution  of  the  formations,  which 
gives  a clue  to  the  presence  of  overlaps,  and  (2)  of  the  fossils,  which 
indicate  time  breaks.  The  evident  angular  unconformities  are  be- 
tween the  Vaqueros  (lower  Miocene)  and  Tejon  (Eocene)  at  various 
localities,  between  the  Tejon  and  the  older  Cretaceous  shale  at  points 
on  Reef  Ridge,  between  the  Vaqueros  and  Cretaceous  in  the  Alcalde 
Hills  and  on  Juniper  Ridge,  between  the  Santa  Margarita  (upper 
middle  Miocene)  and  Vaqueros  where  the  Castle  Mountain  fault  zone 
crosses  Reef  Ridge;  between  the  Santa  Margarita  and  Tejon  at  the 
same  point  and  also  at  the  San  Joaquin  coal  mine,  and  between  the 
Santa  Margarita  and  Cretaceous  along  the  north  and  east  sides  of 
McLure  Valley.  Somewhat  more  doubtful  is  the  apparent  discrep- 
ancy between  the  Paso  Robles  (Pliocene-Pleistocene)  and  Etchegoin 
(upper  Miocene)  north  of  Zapato  Creek.  Elsewhere  the  formations, 
even  those  profoundly  distinct  in  age,  generally  appear  conformable 
in  dip. 

Overlaps  of  all  of  the  Tertiary  formations,  except  the  Paso  Robles, 
upon  the  Cretaceous  occur  within  the  Coalinga  district,  thus  proving 
their  mutual  unconformity.  Except  in  the  overlap  of  the  Etchegoin 
on  White  Creek  and  of  the  Vaqueros  in  the  Alcalde  Hills  over  the 
upper  Cretaceous  (Chico)  sandstone  these  overlaps  take  place  over 
the  lower  portion  of  the  rocks  mapped  as  Knoxville-Chico.  The 
variability  of  the  formations  in  original  areal  extent  and  in  thickness, 
lithologic  character,  and  structure  within  small  areas  gives  an  indica- 
tion of  the  local  activity  of  the  disturbing  forces  which  have  continued 
to  act  within  this  region. 

MAIN  LINES  OF  STRUCTURE. 

Coalinga  anticline  and  syncline. — Among  the  individual  features  of 
the  structure  in  the  Coalinga  district  the  Coalinga  anticline  is  next 
in  importance  to  the  general  monocline  on  the  eastern  face  of  the 
Diablo  Range.  This  anticline  is  one  of  the  principal  oblique  struc- 
tures of  the  range.  It  forms  Joaquin  Ridge  and  plunges  toward  the 
valley,  exposing  in  turn  the  Franciscan  formation  at  the  head  of 


GEOLOGY. 


65 


Joaquin  Ridge  and  all  of  the  subsequent  formations.  The  synclinal 
axis  of  its  plunge  occurs  at  Polvadero  Gap,  beyond  which  it  is  un- 
doubtedly continued  by  the  anticline  plunging  in  the  opposite 
direction,  which  causes  the  beds  to  dome  up  into  the  Kettleman 
Hills.  At  the  southern  end  of  these  hills,  about  a mile  south  of  the 
area  mapped,  the  anticline  does  not  plunge  beneath  the  surface  of  the 
valley  again  as  might  be  expected  by  analogy.  On  the  contrary,  it 
exposes  a fairly  low  portion  of  the  Etchegoin  formation  and  the  hills 
are  left  incomplete,  their  cessation  being  due  to  erosional  removal 
rather  than  to  structure,  as  at  the  northern  end.  The  Lost  Hills, 
which  are  situated  within  10  miles  south  of  the  edge  of  the  area 
shown  on  the  map,  have  not  as  yet  been  studied,  but  it  is  a probable 
supposition  that  they  are  due  to  a continuation  of  the  Coalinga  anti- 
cline. The  length  of  this  within  the  district  is  60  miles.  Its  principal 
features  are  its  alternating  plunges  in  different  directions;  its  curving 
course,  indicating  a complexity  in  the  forces  which  have  acted  upon 
it;  its  asymmetry,  and  its  broad  summit  and  steep  flanks.  The  steep 
dips  on  its  southwestern  flank  north  of  Coalinga,  as  compared  with 
the  gently  dipping  summit  and  northeastern  flank,  are  very  pro- 
nounced. Similar  asymmetry  is  observable  in  the  northern  part  of  the 
Kettleman  Hills,  although  the  divergence  in  dip  on  the  two  flanks  is 
not  so  great,  the  usual  maximum  dip  being  35°  to  45°  on  the  south- 
west and  25°  to  31°  on  the  northeast.  The  Coalinga  syncline  is  the 
parallel  supplementary  feature  and  forms  the  topographic  depression 
of  Pleasant  Valley  and  Kettleman  Plain.  Like  the  anticline,  it 
plunges  southeastward  from  Joaquin  Ridge  and  rises  again  opposite 
the  Kettleman  Hills.  West  of  Oil  City  it  dies  out  in  low  dips  on  the 
flank  of  the  anticline. 

The  folds  and  faults  forming  the  other  main  spurs  of  the  Diablo 
Range  in  this  district  have  already  been  mentioned  in  the  discussion 
of  the  topography. 

Los  Gatos  and  White  Creek  basins. — The  structure  in  the  basin  of 
Los  Gatos  and  White  creeks  between  Joaquin  and  Juniper  ridges  is 
peculiar  and  complicated.  A broadly  folded  anticline  of  Cretaceous 
beds  with  a locally  sharp  axis  plunges  southwest  and  northeast  off 
the  flanks  of  these  two  ridges  toward  the  lower  part  of  Los  Gatos 
Creek,  where  it  is  crossed  by  a broad  syncline  plunging  both  north- 
westward into  the  axis  of  the  White  Creek  basin  and  southeastward 
into  Pleasant  Valley.  The  syncline  becomes  sharply  defined  and 
regular  along  White  Creek  where  it  incloses  a remnant  of  Etchegoin. 
Toward  Pleasant  Valley  it  broadens  out  to  form  part  of  the  general 
monocline  dipping  toward  the  axis  of  the  Coalinga  syncline.  A com- 
plicated set  of  faults  occurs  along  Los  Gatos  Creek,  where  the  upper 
sandstone  of  the  Cretaceous  (Chico)  near  the  axis  of  the  syncline  on 
52332— Bull.  357—08 5 


66 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


its  southwestern  side  is  faulted  down  into  contact  with  the  older 
Cretaceous  shale  beds  on  the  southwest  side  of  the  main  fault  line. 
The  movement  has  been  in  the  nature  of  a flattening  of  the  axis  of 
the  syncline  toward  its  head,  resulting  in  the  formation  of  branch 
faults  on  the  downthrow  side  and  greater  and  greater  throw  in  the 
successive  blocks  toward  the  southeast.  Many  small  faults  occur 
that  have  not  been  shown  on  the  map,  and  there  are  doubtless  other 
large  ones  that  have  not  been  observed.  The  basin  of  Los  Gatos 
and  White  creeks  has  probably  been  an  axis  of  movement  along 
which  successive  disturbances  have  taken  place  during  a long  period. 

Alcalde  Canyon. — Another  old  zone  of  movement  is  represented  by 
the  southeastern  face  of  Curry  Mountain  and  the  lower  part  of 
Alcalde  Canyon  from  Alcalde  toward  Pleasant  Valley,  and  possibly 
likewise  out  across  the  valley  toward  Polvadero  Gap.  The  region 
north  of  this  zone  has  had  in  some  respects  a different  history  from 
that  to  the  south,  and  it  is  difficult  to  correlate  the  features  of  the 
geology  in  the  regions  so  separated.  To  the  south  the  formations 
have  a far  greater  thickness,  the  upper  sandstone  (Chico)  portion 
of  the  Knoxville-Chico  rocks  is  lacking,  the  shales  of  the  Santa 
Margarita  (?)  appear  and  gradually  thicken  and  are  only  doubtfully 
to  be  correlated  with  the  Santa  Margarita  formation  to  the  north, 
and  a great  thickening  of  the  Paso  Robles  formation  is  steeply  tilted 
and  well  exposed. 

Jacalitos  Hills. — Between  Alcalde  and  Reef  Ridge  there  is  a 
depressed  area  occupied  by  comparatively  low,  rolling  hills  that 
represents  the  structural  continuation  of  the  old  synclinal  basin  of 
Waltham  Valley.  The  syncline  of  that  valley  plunges  toward  the 
southeast  and  dies  out  just  within  the  area  mapped  on  the  general 
monocline  dipping  away  from  Reef  Ridge.  This  monocline  is  regular 
except  for  some  low,  broad,  plunging  folds  that  throw  it  into  undula- 
tions northwest  of  Zapato  Creek,  among  them  being  the  Jacalitos 
anticline  and  syncline.  A noteworthy  feature  of  the  Jacalitos  anti- 
cline is  that  it  plunges  in  both  directions  into  the  flank  of  the  Jaca- 
litos syncline. 

Castle  Mountain  fault  zone. — The  main  structural  features  of  the 
southwestern  part  of  the  territory  mapped  are  the  Castle  Mountain 
fault  zone,  Pyramid  Hills  anticline,  Avenal  syncline,  and  Diablo 
anticline.  The  Castle  Mountain  is  a very  important  and  complicated 
zone  of  faulting  that  affected  the  Vaqueros  and  older  formations. 
The  downthrown  side  is  on  the  northeast.  Faulting  along  the  same 
zone  is  the  cause  of  the  prominent  scarp  of  Castle  Mountain,  farther 
west.  Within  the  area  mapped  the  movement  took  place  probably 
before  the  beginning  of  Tertiary  time,  leaving  the  fault  scarp  as  the 
shore  line  during  the  Tejon  (Eocene)  and  Vaqueros  (lower  Miocene) 


GEOLOGY. 


67 


epochs.  The  fault  is  not  exposed  east  of  Reef  Ridge  because  covered 
by  the  later  formations.  The  lowest  of  these,  the  Santa  Margarita, 
is  only  very  slightly  wrinkled  at  this  point,  showing  that  practically 
all  movement  along  this  part  of  the  Castle  Mountain  fault  ceased 
before  the  upper  Middle  Miocene. 

Pyramid  Hills  anticline. — The  Castle  Mountain  fault  zone  is  the 
locus  of  an  important  anticlinal  fold  that  was  formed  during  the 
Pleistocene  long  after  the  cessation  of  fault  movement  along  the 
eastern  portion  of  the  zone.  The  Santa  Margarita  and  younger 
formations  have  been  worn  off  over  the  summit  of  the  fold  and  the 
rocks  exposed  along  this  uncovered  axis  belong  in  part  to  the 
Knox vill e-Chico,  but  some  strange  varieties  differing  from  any 
observed  elsewhere  occur  and  have  not  been  identified  as  belonging 
to  any  known  formation.  The  disturbance  of  the  pre-Santa  Margarita 
rocks  has  been  so  great  that  the  axis  of  the  anticline  is  not  easily 
traceable  within  the  faulted  zone.  To  the  southeast  the  general  zone 
of  faulting  gives  place  along  a divergent  axis  to  an  overturned  anti- 
cline in  the  Knoxville-Chico  rocks,  and  this  is  traceable  into  a regular, 
sharp  fold  covered  by  the  shale  of  the  Santa  Margarita.  This  is  the 
anticline  forming  the  prominent  ridge  of  the  Pyramid  Hills  and  the 
northeastward-tilted  monocline  of  Reef  Ridge  and  the  Kreyenhagen 
Hills. 

Avenal  syncline. — On  its  southwest  flank  the  Pyramid  Hills  anti- 
cline dips  down  into  the  Avenal  syncline,  which  determines  the  posi- 
tion of  McLure  Valley.  North  of  Avenal  Creek  this  syncline  is  an 
extremely  sharp  fold,  overturned  and  much  disturbed  beyond  the 
area  mapped,  but  gradually  plunging  and  becoming  shallower  toward 
McLure  Valley. 

Diablo  anticline. — Southwest  of  the  valley  the  beds  rise  again  steeply 
on  the  flank  of  the  Diablo  anticline,  which  is  a steep  fold  plunging 
rapidly  toward  the  southeast  and  forming  Avenal  Ridge,  the  end  of 
the  Diablo  Range.  Its  axis  was  once  overarched  by  the  Santa 
Margarita  and  later  formations,  but  is  now  denuded  of  these  forma- 
tions and  exposes  greatly  disturbed  Knoxville-Chico  rocks.  This 
anticline  is  one  of  the  main  axial  folds  of  the  Diablo  Range. 

o 

CHARACTER  OF  THE  FOLDS  AND  FAULTS. 

The  structural  features  in  this  region  are  almost  invariably  plunging 
and  curving.  Most  of  them  represent  important  and  continuous 
structural  lines  along  which  movements  of  locally  variable  amount  and 
direction  have  taken  place.  The  anticlines  are  as  a rule  asymmetric 
elongated  domes,  the  summits  being  broad  and  the  dips  increasingly 
steep  away  from  the  axis,  but  having  varying  limits  of  angle  on  the 
two  sides  and  at  different  points  along  the  longitudinal  extent  of  the 


68 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


fold.  The  synclines  have  a reciprocal  character.  Several  of  the 
anticlines,  notably  the  Coalinga,  Jacalitos,  and  Pyramid  Hills  anti- 
clines, are  so  formed  that  an  axis  may  be  traced  on  one  or  the  other 
flank  along  which  is  a marked  steepening  of  the  dip  away  from  the 
summit  of  the  fold.  This  indicates  an  inclined  position  for  the  main 
axis  of  the  fold.  An  overturn  occurs  in  the  inclined  axis  of  the 
Coalinga  anticline  at  one  point  along  Oil  Canyon,  and  overturns 
occur  likewise  along  the  Pyramid  Hills  anticline,  the  Avenal  syncline, 
and  on  the  northeastern  flank  of  the  Diablo  anticline.  An  important 
feature  of  the  structure  of  the  district  is  that  the  northern  portion  of 
the  axis  of  the  Coalinga  anticline  and  the  axis  of  the  Jacalitos  anticline 
lean  toward  each  other,  the  former  toward  the  southwest  and  the 
latter  toward  the  northeast,  as  if  due  to  a compressional  force  from 
the  two  sides  toward  the  Coalinga  syncline.  The  Pyramid  Hills 
anticline  is  analogous  in  this  respect  to  the  Coalinga  anticline  north- 
east of  Pleasant  Valley,  and  seems  to  be  opposed  in  a similar  way 
across  McLure  Valley  by  a contrary  thrust  in  the  Diablo  anticline. 
The  two  latter  folds  have,  however,  not  been  studied  in  detail. 

In  regard  to  the  character  of  the  faults  in  this  region  little  can  be 
said,  owing  to  the  fact  that  the  areas  of  older  rocks  in  which  they 
chiefly  occur  were  examined  only  in  a reconnaissance  way.  In  the 
case  of  the  Los  Gatos  Creek  and  Castle  Mountain  fault  zones  the 
planes  of  movement  have  been  many  and  the  resultant  downthrow 
in  each  case  is  on  the  northeast. 

THE  OIL. 

OCCURRENCE. 

The  petroleum  in  the  Coalinga  district  occurs  in  four  different  for- 
mations, the  Tejon  (Eocene)  , Vaqueros  (lower  Miocene),  Santa  .Mar- 
garita (upper  middle  Miocene),  and  Jacalitos  (upper  Miocene).  In 
the  first  the  oil  is  thought  to  be  primary — that  is,  it  is  believed  to 
have  originated  in  the  formation ; in  all  of  the  others  it  is  secondary — 
that  is,  it  has  come  into  them  from  some  outside  source  since  their 
formation. 

OIL  ZONES. 

Geologic  'position . — Within  each  of  the  formations  are  one  or  more 
oil-bearing  zones,  consisting  either  of  more  or  less  extensive  layers  of 
sand  or  gravel,  which  can  be  traced  in  a general  way  over  large  areas, 
or  of  local  lenses  of  the  same  materials.  The  oil  sands  in  the  Tejon 
(Eocene)  will  be  referred  to  collectively  as  the  Tejon  oil  zone;  those 
in  the  lower  part  of  the  Vaqueros  as  the  lowest  Vaqueros  zone,  or 
zone  D;  those  in  the  middle  Vaqueros  (Eastside  field  light-oil  sands) 
as  the  light-oil  zone,  or  zone  C;  those  in  the  upper  Vaqueros  (first 
sand)  in  the  fields  northeast  of  Los  Gatos  Creek  and  in  the  lower 
Jacalitos  in  the  Westside  field  south  of  Los  Gatos  Creek  as  zone  B; 


THE  OIL. 


69 


and  those  in  the  Jacalitos  in  the  Westside  held  above  the  productive 
basal  beds  of  that  formation  as  zone  A.  The  top  of  zone  B is  shown 
in  contour  on  PI.  II.  With  the  exception  of  those  in  the  lowest  zone 
in  the  Vaqueros  (zone  D)  the  oil  sands  are  known  to  consist  in  many 
places  of  more  or  less  local  beds  or  lenses  showing  abrupt  differ- 
ences in  thickness,  composition,  grain,  and  hardness  from  well  to 
well,  often  with  a puzzling  diversity  in  gravity  of  product  within 
short  distances.  Zone  D,  as  would  be  expected  of  the  basal  portion 
of  a widely  spread  formation,  partakes  of  the  same  general  character- 
istics throughout  nearly  its  entire  range  within  the  district — that  is, 
it  is  usually  coarse  gravel  at  the  base,  with  somewhat  finer  gravel  or 
very  coarse  sand  above  this,  and  finally  medium-grained  sand.  The 
productive  beds  in  the  other  zones  vary  from  medium  fine-grained 
to  coarse  pebbly  sand  or  even  gravel. 

Tejon  oil  zone. — The  sandstones  underlying  the  shale  of  the  Tejon 
(Eocene)  formation  or  interbedded  with  its  basal  members  contain 
commercial  quantities  of  oil  on  the  Coalinga  anticline  in  the  Oil  City 
field,  and  also  at  several  points  on  the  flanks  of  the  great  steep- 
dipping monocline  in  the  Kreyenhagen  field.  Many  oil  seepages 
occur  along  the  outcrops  of  these  sands,  and  it  was  the  inducement 
offered  by  these  seepages  in  the  Oil  City  region  that  led  to  the  drill- 
ing of  the  test  wells  from  which  the  present  district  has  been  devel- 
oped. The  oil  in  the  Tejon  is  usually  of  light  gravity,  about  33°  to 
34°  B.,  and  greenish  in  color.  The  thickness  of  the  productive  sands 
is  ordinarily  between  15  and  60  feet,  and  the  yields  are  light,  4 to 
75  barrels  per  well  per  day  being  the  normal  extremes  of  production, 
although  the  initial  flow  of  one  of  the  Oil  City  wells  is  said  to  have 
been  700  barrels  per  day. 

Vaqueros  oil  zones. — The  principal  oil-bearing  formation  in  the 
Coalinga  district  is  the  Vaqueros  or  lower  Miocene.  It  yields  prac- 
tically all  of  the  oil  in  the  Eastside  field,  a considerable  part  of  that 
from  the  Westside  field,  and  is  thought  to  contain  commercially 
important  quantities  in  the  Kreyenhagen  field  and  in  the  region  of 
the  Kettleman  Hills.  The  total  distance  penetrated  through  this 
formation  by  the  wells  in  the  Eastside  field  is  about  700  feet,  and  in 
the  Westside  between  300  and  500  feet.  The  actual  productive 
sands  of  course  occupy  only  a relatively  small  space  in  this  column, 
usually  less  than  150  feet  in  the  Eastside  and  less  than  100  feet  in 
the  Westside.  Three  zones  are  recognized  in  this  formation,  the  low- 
est, or  zone  D,  the  middle,  or  zone  C (productive  only  in  certain 
parts  of  the  Eastside  field,  where  it  yields  oil  up  to  31°  B.  in  gravity), 
and  zone  B,  recognized  as  Vaqueros,  in  the  Eastside  field  and  in  the 
northern  part  of  the  Westside  field.  The  oil  from  the  Vaqueros 
varies  in  gravity  from  14°  to  22°  in  the  Westside  and  from  14°  to  31° 
in  the  Eastside.  It  is  black  or  dark  brown  and  the  production 
averages  between  100  and  200  barrels  per  well  per  day.  One  well 


70 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


in  the  Eastside  field  is  now  flowing  3,000  barrels  of  oil  per  day,  and 
an  initial  yield  of  7,000  barrels  in  eighteen  hours  was  recorded  for 
another  well  in  the  same  field,  but  these  figures  are  unusual. 

Santa  Margarita  oil  zone. — A stratum  of  sand  carrying  character- 
istic fossils  of  the  Santa  Margarita  formation  immediately  overlies 
the  Tejon  in  the  region  of  the  San  Joaquin  coal  mine  in  the  Westside 
field,  but  is  so  closely  associated  with  lithologically  similar  beds  of 
the  Jacalitos  in  the  same  vicinity  that  it  has  been  mapped  and  dis- 
cussed with  them  as  zone  B.  The  persistent  stratum  of  fine  blue 
sandy  shale  found  throughout  the  Eastside  field  and  known  locally 
as  the  1 1 Big  Blue,  ’ ’ is  arbitrarily  placed  in  the  Santa  Margarita  for- 
mation. The  “Big  Blue”  immediately  overlies  the  uppermost 
Yaqueros  oil  zone,  zone  B,  the  top  of  which  is  shown  in  contour  on 
the  map  (PI.  II). 

Jacalitos  oil  zones  ( A and  B). — The  Jacalitos  (upper  Miocene) 
formation  is  productive  throughout  the  Westside  field,  except  at  the 
extreme  southern  and  northern  ends  and  in  those  wells  distant  over 
a mile  or  so  from  the  outcrop  of  the  sands.  In  other  words,  the 
formation  is  commercially  oil  bearing  wherever  it  rests  upon  or  is 
relatively  near  to  the  Tejon  formation,  the  source  of  the  oil. 

Two  oil  zones  are  recognized  in  the  Jacalitos,  the  lower,  or  zone  B, 
which  is  the  productive  zone  over  the  southwestern  part  of  the  West- 
side  field,  and  zone  A,  situated  some  200  feet  above  zone  B,  which 
carries  tar  sands  or  poorly  saturated  oil  sands.  The  two  zones  are 
generally  separated  by  sulphur  water — the  “big  sulphur ’’—although 
the  most  persistent  sulphur  water  in  the  northern  end  of  the  West- 
side  field  overlies  zone  A.  Northward  in  the  Westside  field  the 
productive  sands  of  zone  B are  found  lower  and  lower  in  the  series 
of  beds  until  in  the  northern  end  the  oil  is  believed  to  come  from 
beds  in  the  uppermost  Yaqueros,  just  below  the  base  of  the  upper 
Miocene  (either  Santa  Margarita  or  Jacalitos). 

ACCUMULATION  OF  THE  OIL. 

The  influence  of  structure  on  the  accumulation  of  the  petroleum 
varies  somewhat  for  different  parts  of  the  field,  the  variation  being 
due,  it  is  believed,  to  the  presence  or  absence  of  water  beneath  the 
oil  zones  in  the  various  areas.  In  general  the  oil  in  the  Tejon  (Eocene) 
is  accompanied  by  water  in  the  underlying  beds,  and  possibly  also  in 
the  oil  sands  far  down  on  the  dip;  under  these  circumstances  the 
anticlinal  theory®  of  accumulation  seems  to  hold  good.  A modified 

a The  anticlinal  theory  of  oil  accumulation  assumes  that  the  oil,  being  of  less  specific  gravity,,  rises 
above  the  water  present  in  porous  rocks  and  collects  at  the  highest  possible  points  in  upward  folds, 
being  there  confined  by  impervious  strata  arching  over  the  folds.  The  presence  of  water,  according 
to  this  theory,  is  considered  as  fundamentally  necessary  for  the  carrying  out  of  the  process  of  accumu- 
lation in  anticlines.  For  a fuller  discussion  of  this  subject  see  Arnold,  R.,  and  Anderson,  R.,  Geology 
and  oil  resources  of  the  Santa  Maria  oil  district,  Santa  Barbara  County,  Cal.:  Bull.  U.  S.  Geol. 
Survey  No.  322, 1907,  pp.  71  et  seq. 


THE  OIL. 


71 


form  of  the  same  theory  is  apparently  applicable  to  certain  mono- 
clines, in  which  water  is  associated  with  oil,  such  as  those  in  the 
Westside  and  Kreyenhagen  fields,  where,  instead  of  impervious  beds 
overlying  the  porous  sands,  the  residual  tar  or  heavy  hydrocarbons 
left  upon  evaporation  of  the  lighter  substances  originally  in  the  con- 
tained petroleum  seal  the  outcrops  and  hinder  or  prevent  the  escape 
of  the  oil  from  below. 

Where  no  water  exists  in  or  is  associated  with  an  oil  zone,  as,  for 
instance,  in  the  deeper  portions  of  the  Westside  field  and  in  by  far  the 
greater  part  of  the  Eastside  field,  structure  apparently  plays  but  a 
minor  part  in  the  accumulation  of  the  oil,  the  presence  or  absence  of 
the  petroleum  in  the  porous  strata  of  the  zone  apparently  depending 
entirely  upon  the  presence  or  absence  of  the  oil-yielding  shales  of  the 
Tejon  (Eocene)  below  or  near  to  the  beds  in  question.  If  the  Tejon 
is  present  under  any  particular  sand  or  zone,  then  the  abundance  or 
scarcity  of  the  oil  depends  largely  on  (1)  the  proximity  of  the  par- 
ticular sand  to  the  Tejon;  (2)  the  state  of  disturbance  of  the  under- 
lying shale  of  the  Tejon,  or  its  relative  position  (whether  unconform- 
able  or  conformable)  to  the  overlying  beds;  (3)  the  degree  of  porosity 
and  grain  of  the  sands  of  the  zone;  and  (4)  the  effectiveness  of  the 
barriers  hindering  the  escape  of  the  hydrocarbons  (oil  and  gas)  from 
the  oil  sands. 

Within  the  tested  territory  of  the  Coalinga  district  it  has  been 
found  that  the  areas  of  Miocene  sediments  (either  Vaqueros,  Santa 
Margarita,  or  Jacalitos),  immediately  underlain  by  the  shales  of  the 
Tejon,  are  oil  bearing;  that  the  productiveness  of  these  beds  varies 
roughly  inversely  with  their  distance  from  the  Tejon;  and  that  the 
productiveness  is  greatest  where  the  Tejon  occupies  a position  of 
angular  unconformity  with  the  Miocene  sands  or  is  more  or  less  dis- 
turbed, as  near  the  axis  of  an  anticline  such  as  the  Coalinga  anticline. 

GRAVITY  OF  THE  OIL. 

The  gravity  of  the  petroleum  at  any  point  in  any  particular  bed  is 
apparently  influenced  chiefly  by  (1)  the  original  composition  of  the 
oil;  (2)  the  thickness  and  composition  of  the  media  through  which  it 
has  migrated  and  in  which  it  is  detained;  (3)  its  present  or  past 
association  with  water  ; and  (4)  its  present  distance  from  the  outcrop 
of  the  oil-bearing  zone  or  its  depth  below  the  surface,  etc.  Little 
definite  information  is  now  available  concerning  the  effect  of  many 
of  these  factors.  It  seems  in  general,  however,  that  the  oil  loses  in 
gravity  by  migration  either  upward  through  various  strata  or  along 
a particular  bed;  that  it  loses  on  association  with  water;  that  within 
certain  limits  it  decreases  in  gravity  up  the  dip,  owing,  probably,  to 
proximity  to  the  surface,  with  its  accompanying  facilities  for  the 
escape  of  certain  of  the  hydrocarbons:  and  that,  other  things  being- 
equal,  the  finer  the  gram  of  the  containing  reservoir  the  better  the  oil 
will  retain  its  original  quality. 


72 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


RELATIONS  OF  WATER  TO  OIL. 

The  most  important  problem  next  to  that  of  the  actual  occurrence 
of  the  petroleum  in  any  field  is  the  relation  of  the  water  sands  to  the 
sands  containing  the  oil.  One  or  more  sands  carrying  water  are 
almost  invariably  encountered  above  the  Miocene  oil  zones  in  the 
wells  of  the  Coalinga  district.  The  continuity  of  these  sands  can 
seldom  be  traced  far,  and  they  are  believed  to  be  for  the  most  part 
disconnected  lenses  rather  than  far-reaching  beds.  An  examination 
of  the  surface  outcrops  leads  to  the  same  conclusion.  The  contents 
of  these  upper  water  sands  is  believed  to  be  surface  or  secondary 
water — that  is,  water  which  has  percolated  into  them  since  they  were 
tilted  into  their  present  position  and  their  edges  exposed.  This 
secondary  water  is  seldom  under  much  head,  although  in  a few 
instances  it  has  been  known  to  flow  with  considerable  energy. 

One  of  the  most  persistent  layers  or  zones  of  water  is  the  one 
termed  the  uBig  Sulphur/ ’ a malodorous  blackish  fluid  met  with  in 
or  above  zone  A in  the  Westside  field  north  of  Los  Gatos  Creek,  and 
between  zones  A and  B south  of  Los  Gatos  Creek.  No  productive 
oil  sands  are  found  above  this  sulphur-water  sand,  although  one  or 
more  tar  sands  are  sometimes  found;  it  may  therefore  he  considered 
the  limit  of  the  upward  migration  of  the  oil,  at  least  in  commercial 
quantities.  A similar  and  fully  as  persistent  zone  of  sulphur  water 
is  encountered  immediately  above  the  second  oil  zone,  zone  C,  over  a 
large  part  of  the  Eastside  field.  The  sulphur  content  of  these  waters 
probably  bears  an  intimate  relation  to  the  oil,  for  in  all  of  the  seep- 
ages in  this  field  where  the  oil  is  accompanied  by  water  the  latter  is 
heavily  charged  with  sulphur.  However,  not  all  of  the  sulphur 
springs  in  the  region  contain  oil,  so  that  there  is  a possibility  of  the 
sulphur  even  in  this  particular  sand  having  an  origin  independent  of 
the.  petroleum. 

In  all  of  the  wells  in  the  Westside  field  in  which  the  Jacalitos  or 
upper  Miocene  oil  zone  (zone  B)  can  be  recognized  the  latter  is 
immediately  underlain  by  a stratum  of  water.  For  various  reasons 
it  is  thought  that  in  this  case  also  the  water  is  secondary  and  has 
come  into  the  formation  since  the  passage  of  the  oil  from  the  Tejon 
(Eocene)  into  the  Miocene.  With  the  exception  of  a very  limited 
area  in  the  Eastside  field  no  water  has  so  far  been  reported  from  be- 
low the  lowest  Vaqueros  oil  zone  (zone  D),  which  indicates  almost 
conclusively  that  water  was  not  the  elevating  force  for  the  oil  of 
zone  D;  it  also  strengthens  the  conclusion  that  the  water  in  the 
higher  zones  is  surface  water  that  has  percolated  from  the  outcrops 
in  the  local  catchment  basin,  rather  than  primary  water,  that  has 
been  in  the  beds  since  their  deposition,  or  water  that  has  come  up 
from  below  under  hydrostatic  pressure. 


THE  OIL. 


78 


ORIGIN  OF  THE  OIL. 

As  to  the  origin  of  the  oil  in  the  Coalinga  district,  it  can  be  stated 
unequivocally  that  it  comes  from  the  shales  of  the  Tejon  (Eocene) 
formation;  and  it  is  believed  that  it  is  derived  from  the  organic 
material  in  them.  These  shales  are  composed  largely  of  the  tests  or 
shells  of  diatoms  and  Foraminifera,  and  a smaller  number  of  other 
organisms,  in  such  abundance  as  to  fully  warrant  the  assumption  that 
the  animal  and  vegetable  material  that  must  have  been  contained  in 
them  when  deposited  was  adequate  for  furnishing  a quantity  of 
hydrocarbons  and  other  compounds  more  than  equivalent  to  the 
quantity  of  petroleum  found  in  this  field.  The  shales  of  the  Tejon 
are  everywhere  petroliferous,  their  interbedded  sands  productively 
so,  and  wherever  overlain  by  sediments  these  also  are  petroliferous. 
Furthermore,  the  relative  productivity  of  these  overlying  beds  varies 
inversely  with  their  distance  from  the  Tejon.  If  the  shales  of  the 
Tejon  were  simply  the  medium  of  migration  for  the  oil  from  below, 
the  shales  of  the  subjacent  Knoxville-Chico  (Cretaceous)  would  also 
be  expected  to  serve  as  such,  for  they  are  lower  down  stratigrapliically 
and  are  apparently  of  proper  consistency  (clayey  shale)  for  migration 
by  diffusion.  We  would  also  expect  to  find  them  charged  with  oil, 
their  interbedded  sandstones  productive,  and  the  Miocene  overhung 
them  containing  at  least  as  much,  if  not  more,  oil  than  the  same  for- 
mations overlying  the  Tejon.  But  these  postulated  conditions  con- 
cerning the  Knoxville-Chico  (Cretaceous)  do  not  exist.  The  Creta- 
ceous shales  and  sands  have  been  examined  carefully  in  outcrop,  and 
wells  have  been  drilled  into  them  in  several  places,  but  practically 
no  indications  of  petroleum  were  found.  The  Miocene  (Vaqueros, 
Jacalitos,  and  Etchegoin)  sands  overlying  the  Cretaceous  in  a position 
analogous  to  that  of  the  Miocene  overlying  the  Tejon  (Eocene)  yMeld 
oil  only  when  situated  comparatively  near  the  Cretaceous-Eocene 
contact.  This  is  most  significant,  indicating  that  the  Cretaceous  did 
not  yield  the  oil,  but  that  the  latter,  as  would  be  expected,  after 
passing  from  the  Eocene  into  the  Miocene  has  migrated  for  a short 
distance  along  the  strata  of  the  latter  out  over  Cretaceous  beds. 
Other  negative  evidence  pointing  to  the  origin  of  the  oil  in  the  Tejon 
is  presented  by  the  fact  that  there  are  no  faults  of  consequence  within 
the  productive  area  along  which  migrations  from  depths  could  have 
taken  place. 


74 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


THE  OIL  FIELDS. 

SUBDIVISIONS. 

For  convenience  of  discussion  the  Coalinga  district  has  been  roughly 
divided  into  five  fields  or  regions,  and  these  into  lesser  subdivisions  or 
areas.  The  major  subdivisions  are  as  follows:  (1)  The  Oil  City  field, 
lying  in  Oil  Canyon  near  the  north  end  of  the  district;  (2)  the  East- 
side  field,  embracing  the  territory  northeast  of  Oil  Canyon  and  includ- 
ing Anticline  Ridge;  (3)  the  Westside  field,  extending  southeastward 
from  Oil  Canyon  as  far  as  Alcalde  Canyon;  (4)  the  Kreyenhagen 
field,  which  includes  the  Jacalitos  and  Kreyenhagen  hills,  Reef  Ridge, 
and  the  territory  southward  to  the  Kings  County-Kern  County 
boundary;  and  (5)  the  region  of  the  Kettleman  Hills,  extending 
from  the  Guijarral  Hills  southward  to  the  gap  separating  the  Ket- 
tleman from  the  Lost  Hills. 

CONTOUR  MAP. 

EXPLANATION. 

The  contour  map  of  the  Coalinga  field  (PI.  II)  shows  the  structure, 
•boundaries  of  the  more  important  geologic  formations,  and  certain 
culture,  such  as  towns,  section  lines,  and  a few  roads.  The  structure 
in  the  productive  territory  is  indicated  by  contours  showing  the  dis- 
tance above  (marked  by  a plus)  or  below  (marked  by  a minus)  sea 
level  of  the  base  of  the  “Big  Blue”  or  top  of  zone  B in  the  Eastside 
field  and  of  the  top  of  zone  B in  the  Westside  field.  The  contour 
interval  is  100  feet.  By  means  of  this  map  the  direction  and  amount 
of  dip  of  the  strata  in  the  oil-bearing  formation  may  be  calculated 
for  any  point  in  the  field,  and  the  depth  to  the  various  productive 
sands  or  zones  may  be  approximated  for  most  parts  of  the  territory. 

USE  OF  THE  MAP. 

Suppose  it  is  desired  to  find  the  probable  depth  below  the  surface 
of  the  first  productive  sand  at  the  middle  of  the  north  line  of  SE.  \ 
sec.  24,  T.  20  S.,  R.  14  E.  An  examination  of  the  map  will  show 
that  this  point  lies  approximately  on  the  underground  contour  line 
marked  u — 500;”  that  is,  the  top  of  zone  B is  here  about  500  feet 
below  sea  level.  A close  approximation  of  the  elevation  of  the  point 
may  be  had  by  looking  up  the  elevation  for  the  nearest  derrick  (see 
list,  p.  128),  which  happens  to  be  Claremont  No.  4,  elevation  792  feet, 
and  calculating  the  difference  in  elevation,  say  22  feet  lower,  either 
by  the  eye  or  with  an  aneroid  barometer.  The  distance  from  tihe 
surface  to  the  top  of  the  oil  zone  mentioned  would,  therefore,  be 
500  feet  plus  the  770  feet,  or  approximately  1,270  feet.  As  zone  B 


THE  OIL  FIELDS. 


75 


is  the  uppermost  productive  zone  for  this  part  of  the  field,  the  depth 
desired  is  1,270  feet. 

Again,  suppose  it  is  desired  to  find  the  depth  to  the  main  com- 
mercially productive  zone  at  the  center  of  sec.  5,  T.  20  S.,  R.  15  E. 
Proceeding  as  before,  it  is  found  that  the  depth  of  the  uppermost 
zone  is  about  1,460  feet  below  sea  level  and  that  the  elevation  of  the 
point  is  about  950  feet  above  sea  level,  or  that  the  top  of  the  upper- 
most zone  is  about  2,410  feet  below  the  surface.  It  will  be  found, 
however,  by  reading  over  the  text  referring  to  this  part  of  the  field 
that  the  most  productive  zone  is  zone  D,  which  lies  from  300  to  450 
feet  below  the  top  of  the  upper  productive  zone  (zone  B)  in  this 
region.  Therefore  the  distance  to  the  top  of  the  commercially  pro- 
ductive zone  will  be  2,410  feet  plus  300  to  450  feet,  or  between  2,710 
and  2,860  feet. 

Suppose  it  is  desired  to  find  the  dip  or  pitch  of  the  beds  in  the 
NW.  \ sec.  23,  T.  19  S.,  R.  15  E.  An  examination  of  the  contours 
shows  that  the  beds  are  pitching  a little  east  of  southeast  (or  striking 
a little  north  of  northeast),  and  that  the  dip  is  about  850  feet  for 
half  a mile,  or  about  32.5  feet  per  hundred  feet  at  right  angles  to  the 
strike.  The  south  and  east  components  of  this  dip  may  be  calcu- 
lated by  measuring  in  these  directions  instead  of  directty  down  the 
dip  of  the  beds,  which  is  always  at  right  angles  to  the  direction  taken 
by  the  contours. 

BASIS  OF  THE  CONTOUR  MAP. 

The  section  lines  and  other  culture  are  the  result  of  instrument 
work  by  E.  P.  Davis,  of  the  Geological  Surve}L  The  log  of  nearly 
every  well  in  the  field  that  was  either  finished  or  down  any  consid- 
erable distance  on  April  1,  1908,  was  used  in  the  determination  of 
the  underground  structure  and  the  compilation  of  the  data  concern- 
ing the  oil  zones.  All  of  the  obtainable  surface  evidence  of  dip, 
strike,  and  occurrence  of  petroleum  was  also  used  in  the  preparation 
of  this  map.  In  those  places  where  the  surface  and  well-log  evidence 
were  at  variance  the  latter  was  usually  followed.  In  unsymmetrical 
features  like  the  Coalinga  anticline  and  Coalinga  syncline  the  plane 
of  the  axis  of  the  fold  is  not  vertical,  and,  therefore,  the  anticline  as 
indicated  by  the  contours  showing  the  underground  position  of  cer- 
tain zones  will  not  lie  directly  under  the  trace  of  the  same  anticline 
or  syncline  on  the  surface. 

DIFFICULTIES  OF  PREPARATION  AND  DEGREE  OF  ACCURACY. 

After  carefully  plotting  all  of  the  logs  on  a uniform  scale  it  was 
found  that  the  greatest  obstacle  to  overcome  in  the  preparation  of 
the  contour  map  was  the  correlation  of  the  strata  from  one  well  to 


76 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


another  and  from  one  part  of  the  field  to  another.  The  difficulties 
of  such  correlations  are  doubtless  familiar  to  anyone  who  has  tried 
to  work  out  the  underground  structure  of  any  of  the  California  fields. 
It  must  be  said,  however,  that  the  structure  in  the  Coalinga  district 
is  more  regular  and  the  conditions  more  favorable  for  a successful 
study  and  mapping  of  the  underground  geology  than  they  are  in  any 
of  the  other  California  fields  so  far  examined  by  the  senior  author, 
not  excepting  the  Santa  Maria  field,  which  was  studied  in  1906  and 
of  which  an  underground-contour  map  was  prepared.®  The  effort 
has  been  made  to  delineate  on  the  present  map  all  of  the  details  of 
structure  consistent  with  the  use  of  the  well  logs  as  confidential  infor- 
mation, and  to  supplement  these  details  by  showing  for  the  untested 
areas  what  seem  to  be  most  likely  the  conditions  of  underground 
structure.  Within  the  untested  areas  the  underground  contours  are 
of  course  only  hypothetical  and  are  shown  by  broken  lines. 

Regarding  the  degree  of  accuracy  it  may  be  stated  that  the  exact 
elevations  of  practically  all  of  the  wells  in  the  field  were  used  in  the 
preparation  of  the  map.  The  well  logs  are  assumed  to  be  accurate 
to  the  usual  degree — that  is,  ordinarily  to  the  length  of  one  “ screw,” 
or  about  5 feet.  The  factor  of  error  for  the  developed  territory  is 
therefore  small,  but  will  necessarily  increase  with  the  distance  away 
from  the  drilled  ground.  Future  development  will  add  much  to  the 
knowledge  of  this  field,  and  will  show  the  inaccuracies  of  the  contour- 
ing as  here  presented,  but  it  is  hoped  that  the  benefits  which  may 
accrue  to  the  operators  from  a knowledge  of  the  general  structure  of 
the  field  will  compensate  in  a measure  for  the  errors  in  detail  which 
are  to  be  expected  in  a map  based  on  incomplete  data. 

DETAILS  OF  THE  PRODUCTIVE  AREAS. 

OIL  CITY  FIELD. 

LOCATION. 

The  Oil  City  field  occupies  the  territory  of  the  southern  part  of  sec. 
17  and  the  northern  part  of  sec.  20,  T.  19  S.,  R.  15  E.  Conditions  in 
the  territory  immediately  south  of  Oil  City  in  the  southern  part  of 
sec.  20,  which  has  been  tested  but  found  to  be  poorly  productive,  will 
also  be  discussed  with  the  Oil  City  field.  The  Coalinga  Oil  Company 
and  the  Home  Oil  Company  are  the  only  producers  now  operating  in 
the  Oil  City  field. 

GEOLOGY  AND  STRUCTURE. 

The  Oil  City  field  is  situated  within  the  belt  of  shale  and  inter- 
bedded  or  underlying  sands  of  the  Tejon  (Eocene)  formation,  the  oil 
being  obtained  from  the  last-mentioned  beds.  The  proved  productive 

a Bull.  IT.  S.  Geol.  Survey  No.  322,  PI.  X. 


THE  OIL  FIELDS. 


77 


ground  occupies  the  same  general  relation  to  the  plunging  Coalinga 
anticline  as  the  productive  territory  farther  southeast  in  sec.  28;  it 
is  on  the  more  gently  inclined  or  northeastern  flank  of  the  fold.  Sur- 
face dips  of  50°  to  90°  and  even  overturned  dips  occur  throughout 
the  area  along  the  southwestern  limb  of  the  anticline,  while  a surface 
dip  of  32°  is  the  maximum  for  the  northeastern  limb.  The  well  logs 
indicate  a relatively  constant  dip  of  about  26°  (42  to  44  feet  per  hun- 
dred feet-)  southeastward  down  the  axis  of  the  anticline  and  a rela- 
tively slightly  steeper  dip  in  the  beds  immediately  north  of  it  in  the 
productive  territory. 

GEOLOGY  OP  THE  WELLS. 


The  wells  in  the  productive  area  all  start  in  the  brown  shale  of  the 
Tejon  (Eocene),  and  continue  in  brown,  black,  and  blue  shale  to  the 
bottoms  except  where  they  pass  through  the  oil  sand.  From  one  to 
three  sands  are  penetrated.  The  first  is  from  4 to  15  feet  thick  and 
yields  the  lightest  oil,  said  to  run  as  high  as  40°  B. ; gas  is  also  reported 
from  the  first  sand  in  other  wells,  and  in  still  others  it  is  dry.  The 
second  and  third  sands  comprise  a zone  60  to  100  feet  thick;  in  some 
of  the  wells  this  is  petroliferous  throughout  almost  its  entire  distance, 
while  in  others  the  two  sands  are  separated,  the  upper  usually  run- 
ning from  15  to  20  feet  thick  and  the  lower  from  40  to  60  feet. 

A section  of  the  second  and  third  sand  in  the  productive  area  is  as 
follows : 


Section  of  second  and  third  oil  sands,  Oil  City  area. 

Feet. 


Hard  sand 4 

Soft  pay  sand 15 

Very  hard  sand 6 

Alternating  hard  and  pay  sands 47 


72 


All  of  the  sands  are  comparatively  fine  grained.  The  oil  usually 
comes  from  the  softer  sands  and  the  lower  sand  is  generally  the  most 
productive,  although  it  is  entirely  unproductive  in  some  of  the  wells. 
The  wells  vary  in  depth  from  300  feet  to  nearly  1,700  feet,  and  the 
productive  zone  is  reached  at  depths  varying  from  about  250  to  1,500 
feet. 

The  southern  part  of  sec.  20,  T.  19  S.,  R.  15  E.,  has  been  rather 
thoroughly  tested  and,  though  most  of  the  wells  have  yielded  more 
or  less  oil,  they  were  not  deemed  profitable  enough  to  warrant  con- 
tinuous operation.  The  following  log  of  a typical  well  in  the  aban- 
doned territory  shows  the  general  character  of  the  Tejon  formation. 


78  COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Log  of  Phoenix  Oil  Company’s  well  No.  3,  in  SE.  % sec.  20,  T.  19  S.,  R.  15  E.u 


Feet. 

Pink  shale 300 

Sand  with  water 330 

Dark-colored  shale 420 

Sand  with  sulphur  water  and  oil 440 

Dark-colored  shale 500 

White  clay  shale 520 

Oil  sand 535 

Shale 540 

White  shale 560 

Oil  sand 575 


This  well  is  said  to  have  yielded  50  to  60  barrels  of  black  heavy 
oil  (10°  to  12°  B.)  for  a short  time.  This  low  gravity  is  accounted 
for  by  the  disturbed  condition  of  the  strata  which  the  well  penetrated, 
it  being  located  directly  on  the  anticline  and  just  above  an  oil  seepage 
in  the  canyon. 

Well  No.  2 of  the  Phoenix  Oil  Company,  located  about  300  feet 
west  of  No.  3,  struck  the  sand  at  a less  depth,  but  yielded  less  oil. 
No.  1 went  to  1,300  feet,  but  being  southwest  of  the  anticline  never 
produced.  The  above  log  and  the  conditions  described  are  charac- 
teristic of  most  of  the  test  wells  put  down  in  this  area. 

Following  are  descriptions  of  the  wells  that  have  been  put  down 
here  south  of  Oil  City: 

Blue  Goose  Oil  Company’s  well  No.  1;  E.  J NE.  \ sec.  20.  Depth,  2,200  feet  through 
brown  and  blue  shale.  No  oil,  but  much  water.  Abandoned. 

California  Oil  and  Gas  Company’s  well  No.  1;  SE.  ^ sec.  19.  Formation,  principally 
shale.  Abandoned.  Same  company  has  well  in  SW.  £ sec.  20,  also  abandoned. 

Crescent  Oil  Company’s  well  No.  1;  SE.  \ sec.  20.  Depth,  900  feet.  Little  oil  at 
770  feet.  Gravity,  11°  B. 

Mutual  Oil  Company’s  well  No.  1;  SE.  I sec.  20.  Depth,  1,800  feet.  Abandoned. 

New  York  Oil  Company’s  well  No.  1;  SW.  £ sec.  20.  Depth,  1,000  feet,  all  in 
brown  shale.  No  oil.  Abandoned.  Well  No.  2.  Depth,  2,200  feet,  in  brown  shale 
with  few  hard  sand  layers.  No  oil.  Abandoned. 

Selma  Oil  Company’s  well  No.  1;  SE.  ^ sec.  20.  Depth,  1,742  feet.  Little  oil  sand. 

Zenith  Oil  Company’s  well  No.  1;  SE.  ^ sec.  20.  Depth,  2,380  feet.  A little  oil 
sand  at  1,735  feet  yielding  10  barrels  a day  of  amber-colored  oil,  38°  to  42°  B.  gravity. 
Later  it  was  drilled  deeper  and  struck  a large  quantity  of  salt  water  which  rose  to 
within  300  feet  of  the  top  of  the  hole.  The  oil  sand  in  this  well  is  probably  the 
same  as  the  uppermost  sand  in  the  productive  Oil  City  area.  The  occurrence  of  salt 
water  below  this  is  suggestive  of  bottom  or  edge  water  for  the  Tejon  (Eocene)  lower 
oil  sands.  Well  No.  2,  same  as  Selma  No.  1 (?). 


PRODUCT. 

The  production  of  the  wells  in  the  Oil  City  area  varies  from  the 
figure  for  the  initial  output  of  one  well,  said  to  have  been  700  barrels 
of  oil  per  day  for  a short  time,  to  the  daily  run  of  certain  others, 

o Watts,  W.  L.,  Oil  and  gas  yielding  formations  of  California:  Bull.  Cal.  State  Min.  Bureau,  No.  19, 
1900,  p.  140, 


THE  OIL  FIELDS. 


79 


which  now  will  average  not  more  than  4 barrels  a day.  In  several 
wells  the  oil  is  said  to  have  flowed  over  the  top  of  the  derrick  when 
the  oil  sand  was  first  penetrated,  as  a result  of  gas  pressure,  which 
soon  subsided.  All  of  the  wells  have  to  be  pumped  after  a short 
initial  period  of  spontaneous  flow.  The  average  daily  production 
at  present  is  about  20  barrels  per  well.  The  average  normal  rate 
of  decrease  per  well  for  the  field,  disregarding  the  rapid  decrease 
from  the  initial  production,  has  been  between  15  and  20  per  cent 
per  year  since  1900.  The  productiveness  of  the  wells  increases 
down  the  nose  of  the  anticline  toward  the  southeast,  especially  near 
the  axis  of  the  flexure.  This  is  shown  by  the  fact  that  well  No.  3 
of  the  Home  Oil  Company  (the  original  Blue  Goose  well)  and  No.  7 
of  the  Coalinga  Oil  Company  have  been  among  the  best  producers 
in  the  group. 

The  gravity  of  the  oil  varies  from  48°  Baume,  oil  of  which  gravity 
occurs  only  in  small  amounts,  being  reported  to  come  from  the 
uppermost  sand  in  some  of  the  wells  (5  gallons  of  48°  oil  from  one 
well,  it  is  said),  to  the  usual  run,  which  tests  between  33°  and  34° 
Baume.  There  is  apparently  little  variation  in  gravity  between  the 
wells  up  or  down  the  dip  or  along  the  strike.  The  oil  is  greenish  to 
brownish  in  color  and  shows  little  viscosity. 

EASTSIDE  FIELD. 

PEERLESS-CALIFORNIA  DIAMOND-T.  C.  AREA. 

LOCATION. 

This  area  comprises  that  part  of  the  Eastside  field,  wdiich  includes 
the  northeastern  portion  of  sec.  21  and  the  northern  part  of  secs.  22, 
23,  and  24,  extending  to  the  line  between  Tps.  18  and  19  south  at 
the  northern  end  of  the  district.  The  companies  operating  in  this 
area  are  the  Coalinga  Peerless,  Octave  California  Diamond,  Lorene, 
T.  C.,  Wm.  Graham,  Imperial,  Bowling  Green,  and  California  Oil- 
fields, Ltd. 

GEOLOGY  OP  THE  WELLS. 

All  of  the  wells  in  this  area  start  down  either  in  the  Santa  Mar- 
garita or  Jacalitos  formations  (upper  Miocene)  between  the  top  of 
the  “Big  Blue”  and  the  base  of ’the  Etchegoin.  They  all  reach,  and 
some  of  them  entirely  penetrate,  the  Vaqueros  (lower  Miocene) 
formation,  which  includes  the  oil-bearing  zones,  B,  C,  and  D,  of  this 
part  of  the  field.  The  variation  in  the  beds  penetrated  is  quite 
rapid,  as  is  indicated  by  the  logs,  and,  with  the  exception  of  the 
“Big  Blue,”  it  is  seldom  possible  to  trace  a single  stratum  for  more 
than  one-eighth  or  one-fourth  mile. 

The  map  (PI.  II)  indicates  by  contours  the  distance  of  the  base 
of  the  “Big  Blue”  above  or  below  sea  level.  The  “Big  Blue” 


80 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


varies  in  thickness  in  the  wells — if  the  distance  penetrated  be  counted 
as  equivalent  to  the  thickness — from  about  260  feet  at  the  western 
edge  of  the  area  to  over  350  feet  in  deeper  wells  toward  the  east. 
In  fact,  one  of  the  deep  wells  disclosed  a continuous  shale  formation 
for  about  640  feet,  but  it  is  not  believed  that  this  entire  thickness 
is  included  in  the  “Big  Blue”  farther  west.  One  of  the  unique 
characteristics  of  the  “Big  Blue”  for  this  area,  and  also  for  nearly 
the  whole  of  the  rest  of  the  Eastside  field,  is  the  red-shale  layers 
which  are  found  at  various  points  interbedded  with  the  blue  variety. 
The  red  shales  are  well  shown  in  outcrop  in  secs.  3 and  10,  T.  19  S., 
R.  15  E.,  where  owing  to  their  peculiar  tints  they  may  be  seen  for 
a distance  of  several  miles.  The  red  shale  consists  almost  entirely 
of  comminuted  serpentine,  which  is  naturally  green  but  is  turned 
red  by  the  oxidation  of  the  iron,  of  which  serpentine  contains  a rela- 
tively high  per  cent.  The  red  shale  appears  prominently  on  the 
sumps,  where  it  forms  brilliant  coatings  as  the  material  is  dumped 
from  the  bailers. 

Water  sands  from  20  to  175  feet  thick  are  found  just  above  the 
“Big  Blue”  from  the  western  part  of  the  NW.  I sec.  22  eastward  to 
the  deepest  wells.  Lenses  of  water  sand  are  also  reported  in  the 
“Big  Blue”  from  the  middle  of  sec.  14  eastward. 

Seashells  are  another  characteristic  of  the  logs  of  this  part  of  the 
area.  They  occur  from  about  120  feet  above  the  “Big  Blue”  in  the 
Peerless  area  to  230  feet  above  it  in  the  wells  in  sec.  12.  Some  of 
the  deeper  wells  also  show  a layer  of  seashells  about  530  feet  above 
the  “Big  Blue.” 

A more  or  less  persistent  zone  of  sulphur  sands  occurs  from  20  to 
180  feet  above  the  first  productive  zone,  zone  B,  but  is  not  reported 
in  all  the  wells.  Sulphur  water  also  occurs  below  the  productive 
sands  in  two  of  the  wells  only,  while  certain  of  the  Peerless  wells  are 
said  to  yield  no  water  whatever.  These  facts  clearly  indicate  that 
the  water  occurs  in  more  or  less  isolated  lenses  of  sand,  similar,  in 
a general  way,  to  the  lenses  carrying  the  oil. 

Between  the  base  of  the  “Big  Blue”  and  the  first  productive  oil 
sand  (zone  C)  there  is  about  350  feet  of  dry  sand,  shells,  and,  just 
above  the  oil  sand,  some  blue  or  brown  clay  or  shale  layers.  These 
last  are  often  interbedded  with  dry  or  poorly  saturated  oil  sands  (zone 
B,  in  part).  The  thickness  of  the  strata  intervening  between  the 
“Big  Blue”  and  the  top  of  zone  C reaches  450  feet  in  the  deeper  wells 
farther  east  down  the  dip. 

Very  little  regularity  exists  in  the  oil  zones,  as  is  shown  by  the  well 
logs.  The  productive  beds  (zones  C and  D)  consist  of  alternating 
coarse  sands,  fine  gravels,  blue  and  brown  shale  and  shells,  with  coarse 
gravel  at  the  base  of  zone  D.  The  productive  measures  are  usually 


THE  OIL  FIELDS. 


81 


about  225  feet  thick,  measuring  from  the  top  of  the  first  productive 
sand  to  the  brown  Eocene  shale  of  the  Tejon  formation,  and  though 
they  comprise  both  zones  C and  D,  a separation  of  the  two  is  not 
possible  in  many  of  the  wells.  The  total  thickness  in  the  wells  from 
the  base  of  the  “Big  Blue”  to  the  brown  shale  of  the  Tejon  is  a little 
over  600  feet. 

Various  names  have  been  applied  to  certain  individual  sands  that 
have  been  traced  for  short  distances  throughout  this  area.  Among 
these  is  the  “Sauer  Dough”  sand,  which  is  the  uppermost  sand  in 
some  of  the  wells  along  the  western  edge  of  sec.  22.  It  is  usually 
about  10  feet  thick.  About  40  feet  below  the  “Sauer  Dough”  is  a 
40-foot  sand  known  as  the  “Pulaski.”  A careful  comparison  of  the 
logs  in  the  area  shows  that  these  two  sands,  and  others  also  to  which 
local  names  have  been  given,  are  not  traceable  for  any  great  distance, 
although  the  names  have  been  applied  to  various  strata  in  wells  over 
other  parts  of  the  Eastside  field. 

PRODUCT. 

Nearly  all  of  the  wells  in  this  area  have  been  drilled  since  1904,  so 
that  data  concerning  decrease  in  production  are  rather  meager.  The 
production  of  the  wells  varies  from  about  25  to  something  like  700 
barrels,  the  production  increasing  down  the  dip,  other  things  being 
equal.  The  T.  C.  well  in  sec.  22  is  said  to  yield  about  400  barrels  a 
day,  which  is  believed  to  be  a fair  initial  average  of  what  would  be 
encountered  over  most  of  the  area  in  properly  handled  wells  1,500 
feet  or  more  in  depth.  The  average  production  for  the  wells  in  the 
area  is  about  125  barrels  a day.  The  yield  depends  largely  on  the 
handling  of  the  well,  for  holes  going  down  under  practically  the  same 
conditions  give  quite  different  results  under  various  managements. 
One  well  which  had  an  initial  production  of  200  barrels  now  yields  only 
20  to  25  barrels  a day.  This  decrease  is  probably  due  not  entirely  to 
natural  causes  but  to  a sanding  up  of  the  hole.  The  gravity  of  the 
product  from  this  area  varies  from  18°  to  24°  B.  So  many  sands  are 
perforated  that  it  is  usually  impossible  to  tell  the  gravity  of  oil  from 
any  particular  one.  However,  the  uppermost  important  productive 
zone  (top  of  zone  C)  in  the  area  is  believed  to  yield  oil  between  20° 
and  21°  B.  gravity.  The  next  sand,  say  about  80  feet  below  the  first, 
yields  24°  B.  gravity,  or  possibly  slightly  better,  while  the  lowest  sand 
(base  of  zone  D),  which  rests  directly  on  the  shales  of  the  Tejon,  pro- 
duces oil  of  18°  or  20°  B.  gravity. 

Some  of  the  wells  yield  a little  water  with  the  oil,  and  it  is  claimed 
by  some  drillers  that  this  water  comes  from  the  oil  sands,  but  it  is  the 
belief  of  the  writers  that  in  nearly  every  instance  the  water  has  leaked 
in  from  the  surrounding  water  sands  and  is  not  obtained  directly 
52332— Bull.  357—08 6 


82 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


from  the  oil  sands.  Relatively  little  sand  is  yielded  by  the  wells  after 
the  initial  period  of  production,  but  much  trouble  has  been  encoun- 
tered in  some  of  the  deeper  wells  owing  to  the  gas  pressure  forcing  the 
sand  in  from  the  bottom.  Gas  accompanies  the  oil  in  all  of  the  wells 
and  is  also  encountered  alone  in  isolated  pockets,  many  of  which  are 
above  the  productive  zones.  Other  conditions  being  the  same  the 
greater  gas  pressure  occurs  in  the  deeper  wells. 

TECHNOLOGY. 

The  best  success  in  shutting  off  the  water  in  this  area  has  been  in 
landing  the  casing  in  a blue  shale  just  below  the  sulphur-sand  zone. 
Surface  waters  are  shut  off  above  this  with  a larger  casing,  but  the 
purity  of  the  oil  depends  entirely  upon  the  careful  handling  of  the 
lower  waters  immediately  overlying  the  oil  sands. 

STAND ARD-CARIBOU-CALIFORNIA  MONARCH  AREA. 

LOCATION. 

This  area  covers  the  northeastern  portion  of  sec.  27,  the  southern 
part  of  secs.  22,  23,  and  24,  all  of  secs.  25  and  26,  and  the  northern 
part  of  secs.  35  and  36.  The  following  companies  operate  in  this 
area:  California  Oilfields  (Ltd.),  the  Standard,  Caribou,  Associated, 
Twenty-Two,  Record,  Pittsburg,  and  Boston  & California. 

GEOLOGY  OF  THE  WELLS. 

The  wells  in  this  area,  as  in  the  area  farther  north,  start  down  in 
the  Santa  Margarita  and  Jacalitos  (upper  Miocene)  sands  and  shales 
between  the  top  of  the  “Big  Blue”  and  the  basal  Etchegoin.  In  the 
area  where  secs.  21,  22,  27,  and  28  meet,  the  “Big  Blue”  is  about 
220  feet  thick  in  the  wells,  increasing  toward  the  eastern  limit  of  the 
productive  territory  to  about  320  feet.  Red  shales  are  reported  inter- 
bedded  in  the  “Big  Blue”  in  nearly  all  of  the  wells  throughout  the 
area,  apparently  thickening  and  becoming  relatively  more  prominent 
in  the  deeper  wells  toward  the  east  and  north.  Some  white  and 
light-blue  shale  layers  also  occur  in  the  same  zone,  and  in  the  western 
part  of  the  area  gray  and  brown  dry  sands  are  encountered  above  it. . 
From  a point  a short  distance  west  of  the  middle  of  the  line  separating 
secs.  22  and  27  the  same  sands  contain  water  at  various  distances 
above  the  shale. 

All  of  the  strata  from  the  base  of  the  “Big  Blue”  to  the  top  of  the 
Tejon  (Eocene),  embracing  a distance  in  the  wells  of  from  620  feet  to 
over  800  feet,  are  more  or  less  petroliferous  throughout  this  area. 
Three  oil  zones  may  be  defined  within  these  limits.  The  first  zone 
(zone  B,  the  top  of  which  is  shown  on  PI.  II)  begins  immediately  at 
the  base  of  the  “Big  Blue”  and  is  from  100  to  180  feet  thick,  the 
greater  thickness  occurring  in  the  deeper  wells.  In  the  western  part 


THE  OIL  FIELDS. 


83 


of  the  area  zone  B consists  of  dry  sands,  dry  oil  sands,  or  poorly  satu- 
rated oil  or  tar  sands;  farther  east  it  is  commercially  productive  in 
some  of  the  deeper  wells  but  not  in  all.  Where  productive,  as  in  the 
western  part  of  sec.  26,  the  gravity  of  the  oil  in  zone  B is  about 
14°  to  16°.  Below  zone  B and  between  it  and  zone  C the  strata  are 
Jargely  shale  and  dry  sand. 

The  second  and  third  zones  (zones  C and  D)  are  closely  related,  the 
second  being  the  uppermost  important  producer  over  most  of  the 
area.  Zone  C consists  of  medium-grained  sand  yielding  light -gravity 
oil  (24°  B.,  or  better),  is  about  100  feet  thick,  and  begins  about  400 
to  480  feet  below  the  base  of  the  “Big  Blue”  There  are  usually  from 
1 to  4 productive  sands  in  this  zone.  The  lowest  productive  zone 
(zone  D)  rests  directly  on  the  shales  of  the  Tejon  (Eocene),  is  very 
coarse,  consisting  of  pebbly  sand  or  fine  gravel,  and  is  usually  the 
best  producer  as  regards  quantity,  although  the  oil  is  of  but  20°  to 
23°  B.  gravity. 

Sulphur  water  overlies  zone  B in  the  area  north  of  a line  drawn 
south  of  Caribou  Nos.  11  and  10.  Fossil  shells  are  reported  at  the 
base  of  the  “Big  Blue”  in  some  of  the  wells,  while  in  others,  as  in  the 
region  farther  north,  they  occur  about  450  feet  above  the  base  of  the 
“Big  Blue.”  The  sea  shells  in  some  of  the  Caribou  wells  are  found 
just  above  the  oil  sand  and  associated  with  it. 

PRODUCT. 

Most  of  the  wells  in  this  area  also  have  been  begun  since  1904,  so 
that  figures  for  decrease  in  production  are  meager.  All  of  the  pro- 
ductive sands  in  many  of  the  wells  are  perforated  so  that  it  is  often 
impossible  to  tell  the  production  or  gravity  of  any  one  sand.  How- 
ever, the  general  features  of  variation  are  known  and  will  be  indicated. 
The  variation  in  the  initial  production  in  the  wells  is  from  about  150 
to  1,600  barrels  a day,  and  the  average  production  at  present  is  about 
400  barrels.  The  best  producers,  as  a rule,  are  among  the  deeper 
wells,  although  for  one  which  is  well  up  on  the  dip  (SE.  } sec.  21)  an 
initial  yield  of  1,500  to  1,600  barrels  a day  is  reported.  This  well 
obtained  200  barrels  a day  from  the  upper  sands,  but  was  lowered 
into  the  deeper  sands,  where  it  made  its  phenomenal  record.  Besides 
the  one  mentioned  there  are  at  least  two  other  wells  in  the  area  that 
have  produced  more  than  1,000  barrels  a day.  The  average  decrease 
in  production  for  three  years  has  varied  from  about  20  to  40  per  cent, 
but  some  wells  are  said  to  have  held  out  much  better  than  this. 

The  gravity  of  the  oil  in  this  area  varies  from  16°  to  about  24° 
Baume.  The  heavy  oil  comes  from  the  upper  sands  (zone  B),  which 
are  usually  more  productive  in  the  deeper  wells.  A well  in  the  W. 
i sec.  26  is  said  to  have  yielded  600  barrels  of  15°  or  16°  oil  from  zone 
B when  first  drilled.  The  middle  zone  (zone  C)  produces  oil  of  about 


84 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


24°,  while  the  lower,  coarser,  but  generally  more  productive  sands 
(zone  D)  yield  oil  of  21°  to  22°  B. 

Gas  occurs  in  practically  all  of  the  wells.  In  some  of  them  there 
is  sulphur,  but  most  of  them  yield  a good  quality  free  from  this 
element.  The  influence  of  one  well  on  the  pressure  in  another  is  often 
very  marked.  A certain  well,  for  instance,  dropped  off  more  than 
25  per  cent  in  production  when  another  well  within  300  feet  of  it  was 
brought  in. 

STANDARD-CALIFORNIA  OILFIELDS  (SEC.  27)  AREA. 

LOCATION. 

This  area  includes  the  eastern  part  of  sec.  28  and  the  western  part 
of  sec.  27  excluding  the  portion  along  the  southern  line  of  sec.  27. 
The  Standard  and  the  California  Oilfields,  Ltd.,  are  the  only  com- 
panies operating  in  this  area. 

GEOLOGY  OF  THE  WELLS. 

All  of  the  wells  start  down  in  the  Santa  Margarita  (upper  middle 
Miocene)  and  Jacalitos  (upper  Miocene)  formations  (above  the  top 
of  the  “Big  Blue”  and  below  the  base  of  the  Etchegoin),  which 
usually  include  alternating  sands  and  shales  with  occasional  water 
sands.  These  water  sands  as  a general  rule  are  in  the  form  of  lenses 
and  can  seldom  be  traced  in  the  wells  for  more  than  an  eighth  cf  a 
mile. 

The  “Big  Blue”  maintains  a pretty  uniform  thickness  of  about  250 
to  300  feet  throughout  practically  the  whole  of  this  territory.  In  the 
wells  along  the  middle  of  the  line  between  secs.  27  and  28,  there  is  a 
fairly  persistent  stratum  of  water  sand  immediately  overlying  the  “ Big 
Blue.”  There  are  other  water  sands  above  this  lowest  one  in  some 
of  the  wells,  but  none  that  can  be  traced  far.  An  interesting  stratum 
encountered  in  the  wells  beginning  in  the  vicinity  of  the  California 
Oilfields,  sec.  27,  No.  20,  and  extending  down  into  the  northern  part 
of  sec.  34,  is  known  as  the  “St.  Paul  sand.”  It  lies  about  830  feet 
above  the  base  of  the  “Big  Blue,”  or  from  about  150  to  600  feet 
below  the  surface.  It  is  about  30  feet  thick  and  is  hard,  but  is  believed 
by  some  of  the  operators  to  be  capable  of  yielding  commercial  quan- 
tities of  oil,  though,  so  far  as  known,  it  has  never  been  thoroughly 
tested.  This  occurrence  is  rather  puzzling,  as  there  are  no  other  oil 
sands  within  several  hundred  feet  of  it,  and  the  origin  of  its  petroleum 
is  difficult  to  explain. 

The  oil-bearing  formation  in  the  area  under  discussion  extends 
from  the  base  of  the  “Big  Blue”  for  about  655  feet,  as  measured  in 
the  wells,  down  to  the  top  of  the  brown  shale  of  the  Tejon  (Eocene). 
This  distance  between  the  base  of  the  “Big  Blue”  and  the  brown  shale 
is  apparently  regular  over  that  part  of  the  area  which  has  been  tested. 


THE  OIL  FIELDS. 


85 


The  wells  in  the  deep  territory  have  not  penetrated  the  entire  thick- 
ness of  the  oil  sands,  so  that  the  exact  thickness  of  the  sands  is  not 
known  for  wells  far  down  on  the  dip. 

Three  zones  are  recognizable  in  this  series  of  productive  beds.  The 
first  (zone  B)  occurs  at  the  base  of  the  “Big  Blue,”  is  about  15  to  20 
feet  thick,  and  yields  from  30  to  50  barrels  of  21°  oil  in  the  shallower 
wells. 

The  second  (zone  C)  is  about  300  feet  below  the  top  of  the  “Big 
Blue,”  has  a thickness  of  60  feet,  and  produces  daily  from  100  to  over 
1,000  barrels  of  22°  to  24°  oil  per  well.  A group  of  wells  in  the  middle 
of  the  western  part  of  sec.  27  and  in  the  eastern  part  of  sec.  28  produce 
oil  of  from  25°  to  31°  B.,  the  initial  production  of  the  wells  varying 
from  125  to  1,900  barrels  per  day.  The  oil  from  zone  C,  in  this  local 
area  of  unusually  light  oil,  is  kept  separate  in  most  of  the  wells,  but 
whether  or  not  all  of  the  yield  from  the  big  producers  in  this  light-oil 
area  comes  from  zone  C is  not  known.  The  sands  in  this  light-oil 
zone  are  finer  grained  than  those  in  the  zone  above  or  the  zone  below. 

The  third  oil  zone  (zone  D)  consists  of  coarse,  pebbly  sands  and  fine 
gravels,  and  extends  practically  from  the  top  of  the  brown  shale  of 
the  Tejon  upward  for  over  100  feet.  Oil-bearing  sands  are  found  at 
practically  all  horizons  in  one  well  or  another  from  the  base  of  zone  C 
to  the  top  of  zone  D,  so  that  a separation  of  the  two  is  necessarily 
more  or  less  arbitrary. 

PRODUCT. 

The  wells  in  this  area  have  all  been  drilled  since  1902.  The  product 
of  those  wells  deriving  their  supply  from  the  upper  sands  (zone  B) 
varies  from  30  to  50  barrels  a day  of  21°  B.  oil.  The  middle  zone 
(zone  C)  yields  from  125  to  1,900  barrels  per  well  a day,  the  gravity 
ranging  from  24°  to  31°  B.  One  well  which  had  an  initial  production 
of  1,900  barrels  a day  in  1904  dropped  to  1,300  barrels  a day  after 
one  and  one-half  years.  Several  of  the  wells  yield  on  an  average 
300  to  400  barrels  a day,  while  another  group  averages  but  125  barrels 
of  26°  B.  oil.  The  third  zone  (zone  D)  yields  oil  of  22°  to  23°  B.  It  is 
the  best  producer,  as  far  as  quantity  goes,  in  this  part  of  the  field. 
The  better  gravity  and  greater  production  in  this  particular  area  is 
believed  to  be  due  to  the  position  of  the  wells  adjacent  to  the  axis  of 
the  anticline,  where  the  Eocene  shales  (Tejon),  from  which  the  oil  is 
derived,  are  much  more  fractured,  and  where,  in  consequence  of  this 
fracturing,  the  oil  is  permitted  to  migrate  more  easily  and  with  less  loss 
in  quality  into  the  overlying  porous  sands.  The  concentration  of  the 
oil  within  the  Tejon,  previous  to  its  emigration,  was  also  doubtless 
accentuated  along  the  anticline  by  the  action  of  the  water  which 
occurs  associated  with  or  immediately  underlying  the  oil  sands  in  the 
Tejon. 


86 


COALINGA  OIL  DISTRICT,  CALIFORNIA, 


The  presence  of  the  light  oil  in  the  finer  sediments  is  believed  to  be 
due  to  the  fact  that  the  lighter  hydrocarbons  can  escape  more  easily 
from  coarser  reservoirs  than  from  fine-grained  ones,  so  that,  when 
once  charged  with  the  oil,  the  finer-grained  sands  allow  it  to  maintain 
its  original  quality  more  perfectly  than  a coarse  sand  would.  As 
would  be  expected,  the  production  under  the  same  pressure  is  con- 
siderably less  in  finer  sediments  than  it  is  in  coarse  sands,  but  the 
length  of  productivity  is  consequently  greater  in  the  former  than  in 
the  latter. 

CALIFORNIA  OILFIELDS  (SEC.  34)-COALINGA-MOHAWK  AREA. 

LOCATION. 

This  area  comprises  the  whole  of  secs.  34  and  35,  T.  19  S.,  R.  15  E., 
and  secs.  1,  2,  3,  4,  11,  and  12,  T.  20  S.,  R.  15  E.  The  California 
Oilfields,  Ltd.,  the  Southern  Pacific,  W.  K.,  Turner,  Claremont,  and 
Coalinga-Mohawk  are  the  companies  operating  in  this  territory. 

GEOLOGY  OF  THE  WELLS. 

As  in  the  other  areas  described,  the  base  of  the  “Big  Blue”  is  the 
horizon  shown  by  the  contours  on  the  map  (PI.  II).  The  wells  in 
the  northern  part  of  the  area  start  down  in  the  Jacalitos  (upper 
Miocene)  beds  immediately  underlying  the  base  of  the  Etchegoin. 
Those  south  of  the  line  marking  the  base  of  the  Etchegoin  start  in 
the  sands  or  clays  of  that  formation.  The  “Big  Blue”  in  the  wells 
of  this  area  varies  from  250  feet  in  thickness  in  the  northwestern 
portion  to  about  380  feet  at  the  southwestern  border.  The  peculiar 
red,  green,  and  light-blue  facies  of  the  shale  that  are  characteristic 
of  the  “Big  Blue” ‘in  the  deeper  wells  farther  north  are  also  .found 
in  the  deep  wells  in  portions  of  this  area.  In  the  northwestern  por- 
tion water  sands  appear  to  be  interbedded  at  the  base  of  the  “Big 
Blue,”  as  are  also  some  tar  and  dry  oil  sands,  with  occasional  gas 
pockets.  There  are  also  other  water  sands  in  the  deeper  wells,  an 
especially  persistent  zone  occupying  a position  about  600  to  800  feet 
above  the  base  of  the  “Big  Blue”  in  the  wells  in  the  southern  part 
of  the  area.  Some  of  the  water  in  this  zone  is  said  to  contain  appre- 
ciable amounts  of  sulphur. 

The  “St.  Paul  sand,”  described  in  the  last  area,  also  occurs  in 
the  northern  part  of  this  territory,  where  it  is  encountered  in  prac- 
tically all  of  the  wells,  in  none  of  which,  so  far  as  the  writers  are 
aware,  has  it  ever  been  tested.  Those  wells  which  have  been  put 
down  to  the  brown  shale  of  the  Tejon  (Eocene)  indicate  that  the 
formation  between  the  base  of  the  “Big  Blue”  and  this  shale  has 
practically  the  same  thickness  of  650  feet  or  thereabouts  that  it  has 
in  the  region  to  the  north.  The  whole  of  this  distance  is  occupied 
by  alternating  sandstones  and  shales,  which  are  more  or  less  pro- 
ductive in  the  various  wells.  The  relations  existing  between  the 


THE  OIL  FIELDS. 


87 


various  oil  sands  in  this  area  are  not  well  known,  but  it  is  believed 
that  the  sequence  of  zones,  including  B,  C,  and  D,  is  similar  to  that 
in  the  area  last  described.  A 10-foot  oil  sand  carrying  17°  B.  oil 
occurs  at  the  base  of  the  “Big  Blue/’  probably  corresponding  to 
the  one  which  yields  a 16°  B.  or  heavier  oil  in  sec.  26,  and  which 
has  been  correlated  with  zone  B.  One  hundred  feet  below  the  “Big 
Blue”  the  second  sand,  possibly  zone  C,  is  penetrated,  this  being 
productive  through  about  20  to  25  feet.  About  400  feet  still  farther 
down  is  the  third  zone  (zone  D),  which  is  believed  to  rest  upon 
the  Eocene  shale  (Tejon).  A thin  layer  of  sulphur  water  is  reported 
in  some  of  the  wells  just  above  this  third  zone,  but  enough  blue  or 
brown  shale  intervenes  to  allow  complete  shutting  off  of  the  water 
before  reaching  the  productive  zone. 

PRODUCT. 

The  wells  in  this  area  are  only  two  or  three  years  old,  but  since 
their  inception  they  have  maintained  a reputation  as  the  biggest 
producers  in  the  field.  The  oil  in  these  wells  is  usually  accompanied 
by  large  quantities  of  gas  under  strong  pressure.  As  an  instance 
of  their  unusual  productiveness,  it  is  said  that  one  well  in  the  north- 
ern part  of  sec.  34  yielded  about  7,000  barrels  of  oil  in  eighteen 
hours.  In  ejecting  this  large  amount  of  fluid  from  the  hole  the 
casing  was  practically  all  torn  out.  This  well  is  now  producing  but 
150  barrels  a day,  which  indicates  that  the  great  production  was 
due  to  the  extremely  high  gas  pressure.  Another  well  near  the 
center  of  the  southern  part  of  sec.  27  is  said  to  have  yielded  4,500 
barrels  of  oil  a day  for  some  little  time.  This  well  is  now  believed 
to  yield  about  3,000  barrels  a day.  The  gravity  of  the  oil  from 
these  big  producers  is  between  23°  and  24°  B. 

Another  well  in  the  northern  part  of  sec.  34  yielded  on  an  average 
about  1,000  barrels  a day  for  over  ten  months.  Still  others  of  these 
wells  ran  from  600  to  800  barrels  a day.  One  well,  which  yielded 
26°  B.  oil  as  long  as  it  flowed,  now  yields  a mixture  of  23°  B.  oil 
when  it  is  pumped.  This  implies  that  the  lighter  oil  is  probably 
under  the  greater  gas  pressure,  and  when  this  pressure  is  removed, 
the  heavy  oil  either  forces  back  the  lighter  fluid  or  allows  only  a 
small  percentage  of  it  to  enter  the  well.  The  lower  zones  (zones  C 
and  D)  in  one  well  are  said  to  yield  a stratum  of  29°  B.  oil  at  the  top, 
22°  B.  in  the  middle,  and  26°  at  the  base,  with  an  average  of  about  28°. 

STANDARD-STOCKHOLDERS-HANFORD  AREA. 

LOCATION. 

This  area  comprises  all  of  sec.  28,  except  the  extreme  eastern  edge, 
which  is  described  in  a previous  section  (p.  84).  The  Standard, 
Hanford,  and  Stockholders  oil  companies  are  the  only  operators. 


88 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


GEOLOGY  OF  THE  WELLS. 

The  “Big  Blue”  in  this  territory  varies  from  about  200  to  230 
feet  thick  in  the  wells.  A layer  of  water  sand  is  found  just  above 
it  in  the  eastern  part  of  the  area,  and  in  one  or  two  instances  lenses 
of  water  sand  have  been  reported  as  occurring  in  the  “Big  Blue” 
itself.  The  oil  strata  extend  intermittently  from  the  base  of  the 
“Big  Blue”  for  about  655  feet  to  the  brown  shale  of  the  Tejon 
(Eocene).  The  first  400  feet  of  the  productive  measures  consists  of 
alternating  gas  sands,  oil  sands,  dry  sands,  and  tar  sands  interbedded 
with  shales  and  clays,  and  has  been  correlated  with  zone  B,  although 
it  is  believed  to  comprise  not  only  the  zone  B of  the  areas  toward 
the  east,  but  the  strata  to  the  top  of  zone  C.  In  the  northwestern 
part  of  the  area  this  upper  zone  is  more  or  less  productive,  some  of 
the  wells  which  produced  from  it  alone  yielding  from  10  to  30  barrels, 
per  day  of  20°  B.  oil. 

One  or  two  persistent  layers  of  water  sand  occur  from  50  to  100  feet 
above  the  base  of  zone  B,  or  above  the  top  of  the  second  or  light-oil 
zone  (zone  C).  Enough  blue  or  brown  shale  intervenes  between 
this  water  sand  and  the  productive  beds  below  to  permit  shutting 
it  off.  Big  oyster  shells  are  reported  in  some  of  the  wells  just  above 
the  second  zone,  these  probably  coming  from  the  same  layer  as  that 
yielding  the  oysters  in  the  Yaqueros  formation  on  Laval  grade.  Zone  C 
consists  largely  of  fine  sand  from  20  to  60  feet  thick  and  yields  oil 
of  about  21°  to  22°  B.  gravity.  The  third  zone,  or  zone  B,  consists 
of  coarse  sand  to  gravel  and  begins  about  100  feet  above  the  brown 
shale  of  the  Tejon  (Eocene).  It  is  productive  throughout  its  entire 
depth,  and  yields  more  than  any  other  of  the  zones  in  this  group  of 
wells.  The  daily  production  varies  from  40  to  300  barrels  per  well 
of  18°  to  22°  B.  oil. 

Toward  the  axis  of  the  anticline  which  bounds  the  present  devel- 
oped territory  on  the  southwest  the  strata  are  more  or  less  irregular, 
on  account  of  the  steep  dips  which  are  developed  by  this  profound 
fold.  The  logs  of  the  wells  along  the  axis  are  quite  irregular  and 
indicate  variable  conditions  in  both  the  dip  and  the  productiveness 
of  the  beds.  Water  is  also  more  troublesome  in  these  wells,  owing, 
it  is  believed,  to  the  disturbed  conditions  of  the  elsewhere  imper- 
vious beds  that  surround  the  water  sands.  There  is  very  little  gas 
in  the  sands  toward  the  western  edge  of  this  area. 

PRODUCT. 

The  wells  in  the  area  under  discussion  are  the  oldest  in  the  Coalinga 
district  except  those  in  the  Oil  City  area,  and  many  of  them  have 
produced  continuously  since  their  inception.  The  first  zone  (zone  B) 
yields  up  to  30  barrels  per  day  of  20°  to  22°  B.  oil;  the  second  (zone  C) 
yields  a somewhat  lighter  oil,  from  21°  to  possibly  23°  B.  and  the 


THE  OIL  FIELDS. 


89 


third  (zone  D)  produces  as  high  as  300  barrels  of  18°  to  22°  oil. 
Some  of  the  wells  yield  sand  from  the  lower  productive  beds  and 
water  is  also  mixed  with  the  oil  in  some  of  the  wells  in  the  broken 
formation  near  the  axis  of  the  anticline.  In  none  of  the  wells  in 
this  area  is  the  water  believed  to  come  from  the  bottom  of  the  oil  zone. 

WESTSIDE  FIELD. 

CALI^CONFIDENCE  AREA. 

LOCATION. 

This  area  is  located  in  the  southwest  corner  of  T.  19  S.,  R.  15  E., 
and  comprises  the  territory  controlled  by  the  following  companies: 
The  California  Oilfields,  Ltd.,  the  Call,  Keystone,  Ajax,  American 
Petroleum,  iEtna  Petroleum,  Commercial  Petroleum,  California  Dia- 
mond, Main  State  (formerly  the  Guthrey) , California  Monarch,  Confi- 
dence, and  Kern  Trading  and  Oil.  The  wells  are  located  on  the 
southeastward-dipping  monocline  of  the  Westside  field  at  a point 
where  the  strike  of  the  beds  begins  to  bend  from  northeastward  to 
eastward  around  the  axis  of  the  Coalinga  svncline. 

GEOLOGY  OF  THE  WELLS. 

All  of  the  wells  start  down  in  the  soft  shales,  sandstones,  or  gravels 
of  the  basal  Etchegoin  or  in  the  upper  Miocene  beds  immediately 
underlying  this.  Toward  the  western  part  of  the  area  the  wells  ap- 
parently penetrate  only  through  the  upper  Miocene  formations.  On 
the  western  side,  that  is,  in  the  deeper  wells  of  the  Call,  California  Oil- 
fields, Ltd.,  and  Commercial  Petroleinn,  the  wells  apparently  reach 
sands  in  the  lower  Miocene  (zone  D)  %hat  are  lacking  or  have  not 
been  reached  in  the  wells  in  the  western  part  of  the  area. 

Zone  B,  the  depth  of  which  below  the  surface  is  indicated  by  con- 
tours on  the  map  (PL  II,  in  pocket),  will  first  be  described.  Toward 
the  western  part  of  the  area  it  contains  the  productive  sands  and  is 
found  from  about  650  to  1,050  feet  below  the  surface.  The  oil  in 
this  zone  is  apparently  under  considerable  gas  pressure,  for  in  nearly 
all  of  the  wells,  even  the  shallower  ones,  the  oil  rises  a considerable 
distance  in  the  casing  when  the  sand  is  first  penetrated.  The  sand 
in  the  shallower  wells  varies  from  10  to  20  feet  in  thickness,  thicken- 
ing toward  the  northeast  from  the  region  of  the  Kern  Trading  and  Oil 
territory.  The  sand  is  medium  grained  to  coarse  and  soft,  and  the 
wells  producing  from  it  yield  large  quantities  of  sand  with  the  oil, 
especially  at  first.  Some  of  the  shallower  wells  have  been  known  to 
flow  when  first  brought  in.  F arther  east,  in  the  vicinity  of  the  eastern 
Confidence  wells  and  those  of  the  Main  State  or  Guthrey  leases,  the 
zone  is  apparently  irregular  and  some  of  the  logs  of  the  wells,  although 
reporting  a production  from  the  horizon  at  which  the  sands  are  found 
farther  up  on  the  dip,  do  not  mention  the  thickness  of  the  sands  within 


90 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


the  zone.  Guthrey  No.  1,  which  was  the  biggest  gusher  of  this  part 
of  the  field,  might  be  mentioned  as  an  illustration  of  the  irregularity. 
The  behavior  of  this  well  was  quite  unusual  and  the  exact  location 
of  the  sand  producing  the  gas  and  oil  which  flowed  so  strongly  at  first 
is  doubtful.  Enough  sand  was  ejected  from  this  well  to  cover  the 
derrick  floor  and  the  surrounding  ground  over  6 feet  deep. 

In  the  deeper  wells  zone  B is  apparently  represented  by  two  sands 
which  are  separated  in  some  instances  by  a waxy  clay.  The  total 
thickness  of  the  sand  in  these  wells  runs  as  high  as  50  feet.  Still 
farther  down  the  dip,  or  in  the  deepest  wells  in  the  area,  zone  B ap- 
parently becomes  unproductive,  although  it  yields  evidences  of  gas 
and  petroleum  in  small  quantities.  In  one  of  the  wells  this  zone  was 
pumped  for  three  weeks,  but  the  operators  concluded  that  there  was 
water  in  it  and  abandoned  their  efforts. 

About  200  to  300  feet  above  zone  B is  a zone  of  tar  sands  (zone  A), 
which,  as  the  name  implies,  are  either  dry  or  yield  oil  of  heavy  gravity. 
These  sands  vary  in  number  and  thickness  from  well  to  well,  although 
the  zone  as  a whole  is  fairly  persistent  over  the  entire  area.  Sulphur 
water  occurs  within  zone  A,  usually  at  the  base  of  the  first  tar  sand, 
and  at  some  of  the  wells  it  is  found  at  two  horizons  within  the  zone. 
The  thickness  of  the  tar  sand  varies  from  a minimum  of  10  feet  in 
some  of  the  moderately  deep  wells  to  nearly  100  feet  or  possibly  more 
in  those  farthest  up  on  the  dip.  Thicknesses  approaching  100  feet 
are  also  occasionally  met  with  in  the  deep-well  area. 

About  200  feet  above  the  zone  of  the  tar  sands  (zone  A)  is  a very 
persistent  stratum  of  water.  This  water  is  mineralized  in  all  of  the 
wells  and  in  some  shows  traces  of  sulphur.  Above  this  water  zone 
are  usually  one  or  two  other  water  sands,  the  first  being  only  about 
5 to  10  feet  thick,  but  yielding  considerable  water.  The  second  is 
of  less  importance  and  is  apparently  lacking  in  many  of  the  wells. 

In  the  deeper  wells  toward  the  eastern  part  of  the  area  the  most 
productive  sands  apparently  lie  below  zone  B and  are  believed  to  be 
in  part  the  equivalents  of  the  lower  Miocene  sands  (zones  C and  D) 
which  are  the  productive  sands  of  the  Eastside  field.  The  exact  rela- 
tions of  these  zone  D sands  to  the  overlying  ones  are  perplexing,  but 
it  is  believed  that  zone  D does  not  extend  westward  past  the  middle 
of  the  area  under  discussion,  although  to  the  knowledge  of  the  writers 
no  well  has  yet  been  put  down  which  passes  entirely  through  the 
strata  overlying  the  Tejon  (Eocene)  in  this  part  of  the  field.  Some 
of  the  wells  have  reached  what  they  call  the  black  or  brown  shale,  but 
it  seems  likely  that  these  brown  shales  may  be  simply  petroliferous 
shales  intercalated  in  the  sands  of  the  Vaqueros  (lower  Miocene). 
This  lower  Miocene  sand  zone  (zone  D)  lies  from  100  to  300  feet  below 
zone  B.  Productive  lenses  are  found  at  two  or  three  points  through- 
out the  zone,  but  no  continuous  oil  sands  have  been  definitely  traced 
between  the  wells. 


THE  OIL  FIELDS. 


91 


Taking  the  logs  as  a whole,  they  present  the  following  features 
in  passing  downward  from  the  surface.  First,  the  incoherent  soil 
and  gravel,  then  a thick  series  of  dry  gravels,  sands,  and  shale  or  clay, 
with  occasional  hard  sandstone  shells.  The  first  water  is  encountered 
usually  between  240  and  500  feet.  From  this  downward  two  and 
sometimes  three  other  waters  are  penetrated  before  reaching  the  tar 
sand  zone  (zone  A).  The  zone  of  the  lower  water  sand  or  sands  is 
often  marked  by  numerous  hard  sand  shells.  After  passing  through 
zone  A,  which  varies  from  a few  feet  to  over  300  feet  in  thickness,  a 
200-foot  zone  of  blue  shale  is  encountered.  Below  this  occurs  zone  B 
which  is  characterized  by  medium-grained  to  pebbly  sands,  brown 
shales,  and  several  well-defined  shells.  The  shallower  wells  usually 
stop  at  the  base  of  this  zone,  but  the  deeper  ones  penetrate  some  shale 
and  sands  from  the  bottom  of  zone  B to  the  top  of  the  third  zone, 
which  includes  zones  C and  D and  is  usually  characterized  by  hard 
shells  and  medium-grained  sands. 

* PRODUCT. 

The  production  of  the  wells  in  this  area  varies  from  an  initial  output 
of  20  to  50  barrels  in  the  shallower  wells  to  3,000  or  4,000  barrels  in 
some  of  the  deeper  ones,  such  as  Guthrey  No.  1,  which  was  a pro- 
nounced gusher  when  first  brought  in.  The  daily  average  for  these 
wells  runs  somewhere  between  100  and  200  barrels,  but  some  of  them 
average  as  high  as  300  to  350  barrels  over  long  periods. 

The  gravity  of  the  oil  runs  from  14°  to  nearly  20°  B.,  the  average 
for  the  shallower  wells  being  about  16°",  and  for  the  deeper  wells  some- 
thing like  18°.  The  best  oil  apparently  comes  from  the  middle  zone 
(zone  B),  which  is  believed  to  correspond  in  a general  way  with  the 
light-oil  sands  farther  south  in  the  Westside  field. 

MERCANTILE  CRUDE-S.  W.  & B.  AREA. 

LOCATION. 

This  area  comprises  the  southern  part  of  the  Kern  Trading  and  Oil, 
Confidence,  California  Monarch,  and  E.  W.  Rislev  leases  on  sec.  31, 
T.  19  S.,  R.  15  E.,  the  Fresno-San  Francisco  and  the  northern  parts 
of  the  Cypress  and  Pennsvlvania-Coalinga  properties  in  the  north- 
eastern part  of  sec.  1,  T.  20  S.,  R.  14  E.,  and  the  Mercantile  Crude, 
York-Coalinga,  S.  W.  & B.,  New  San  Francisco  Crude,  and  the 
northern  half  of  Esperanza  in  sec.  6,  T.  20  S.,  R.  15  E.  The  wells  are 
located  on  the  southeast-sloping  monocline  which  dominates  the 
structure  of  the  whole  Westside  field. 

GEOLOGY  OF  THE  WELLS. 

The  wells  in  this  area  all  start  down  in  the  basal  Etchegoin  (upper 
Miocene)  clays,  sands,  gravels,  etc.,  and  the  Jacalitos  (upper  Miocene) 


92  COALING  A OIL  DISTRICT,  CALIFORNIA. 

beds  immediately  underlying  these.  Three  more  or  less  well-defined 
petroliferous  zones  are  developed  in  this  area.  The  top  of  the 
principal  productive  zone  (zone  B)  is  shown  by  contours  on  the  map 
(PI.  II).  In  wells  high  up  on  the  dip  the  sand  in  zone  B is  coarse, 
and  it  usually  contains  pebbles  the  size  of  the  thumb  or  sometimes 
ev£n  larger.  Both  immediately  above  and  below  the  most  productive 
part  of  the  zone  are  sands  in  which  the  oil  is  of  heavier  gravity  than 
that  in  the  most  productive  part.  The  reason  for  this  variation  in 
gravity  between  sands  so  close  together  is  not  at  present  known,  but 
the  variation  may  be  due,  in  part  at  least,  to  variation  in  grain  of  the 
sands.  Farther  down  the  dip  the  sand  becomes  somewhat  thicker, 
but  is  still  quite  coarse  and  in  some  of  the  wells  is  characterized  by 
the  presence  of  shark’s  teeth.  The  coarseness  of  the  sand  and  the 
gas  pressure  are  conducive  to  good  productions,  and  it  is  not  unusual 
for  wells  at  first  to  obtain  as  high  as  300  or  400  barrels  a day  from  this 
one  sand.  In  the  deeper  wells  the  zone  apparently  contains  but  one 
sand,  which  is  in  most  cases  underlain  by  a more  or  less  persistent 
hard  sandstone  shell.  The  gravity  of  the  oil  in  zone  B runs  about 
17°  B.  and  is  apparently  constant  throughout  the  area.  From  50  to 
100  feet  above  zone  B is  a 100  to  200  foot  zone  (zone  A)  of  tar  sands 
similar  to  those  encountered  in  the  wells  toward  the  north.  This  tar 
zone  is  thickest  in  the  northwestern  part  of  the  area,  where  it  consists 
of  from  one  to  three  dry  oil  sands  or  tar  sands,  which  sometimes 
contain  heavy  oil  and  occasionally  water  associated  with  the  oil. 
Eastward,  or  down  the  dip,  the  tar  sand  decreases  rapidly  in  thick- 
ness, until  in  the  deepest  wells  in  the  area  the  tar  zone  is  represented 
by  but  one  or  two  sands  which  never  attain  more  than  10  or  20  feet 
in  thickness.  Immediately  overlying  zone  A is  a persistent  stratum 
of  sulphur  water,  which  is  encountered  in  practically  all  of  the  wells 
in  this  area  and  is  known  in  general  under  the  name  ‘ ‘ big  sulphur  ’ ’•  or 
“main  sulphur.”  Beneath  this  sulphur  water  in  most  of  the  wells  is 
a hard  sand  shell,  which  is  apparently  more  or  less  persistent  through- 
out the  area.  Still  another  sulphur  water  is  encountered  a little 
above  the  lower  one  in  some  of  the  wells,  but  does  not  appear  to  be  as 
persistent  as  the  “main  sulphur.” 

Below  zone  B in  the  deeper  wells  is  still  a third  petroliferous  zone 
(zone  D),  which  may  correspond  in  part  to  the  lowest  zone  in  the  area 
immediately  north.  It  is  penetrated  by  but  two  or  three  wells  and 
its  productiveness  is  more  or  less  uncertain.  In  one  log  this  lower 
sand  is  mentioned  as  brown  shale,  although  the  same  log  shows  that 
the  casing  was  perforated  at  this  point,  thus  indicating  that  the 
formation  was  oil  bearing. 

The  water  sands  in  the  area  are  usually  three  or  four  in  number, 
the  uppermost  being  encountered  at  from  145  to  about  375  feet  in 
depth.  The  first  sand  is  apparently  not  so  productive  as  the  second, 


THE  OIL  FIELDS. 


98 


which  yields  plenty  of  water  in  many  of  the  wells.  Below  the  second 
sand  is  a third  and  sometimes  even  a fourth,  before  the  sulphur  sand, 

immediately  overlying  the  tar  zone,  is  encountered. 

- 

Typical  well  loq  in  Mercantile  Crude-S.  W.  & B.  area. 

Feet. 

Surface  soil  and  incoherent  sand  and  gravel,  followed  by  harder  shales, 

sandstone,  and  gravels 200 

First  water  sand 5-  20 

Shale - 50+ 

Second  water  sand. 

Shale,  sometimes  containing  one  or  more  water  sands 300 

Gravel,  more  or  less  persistent  stratum,  apparently  carrying  water  in  several 
of  the  wells,  especially  those  nearest  the  outcrop. 


Shale - 100 

“Main  sulphur”  water 5-  20 

Tar  sand  (zone  A) 100-200 

Shale 50-100 

Productive  sands  (zone  B) 20-  50 

Shale,  largely  brown 50-200 

Zone  D 20-  50 


The  depths  of  the  wells  in  this  area  vary  from  about  1,000  feet  to 
over  1,700  feet. 

PRODUCT. 

The- production  varies  from  12  barrels  in  the  wells  farthest  west  to 
about  400  barrels  in  the  deeper  and  more  productive  ones.  Large 
quantities  of  sand  usually  accompany  the  oil,  especially  in  those  wells 
high  up  on  the  dip,  and  even  in  some  of  those  which  penetrate  the 
sand  at  much  greater  depth.  The  gravity  of  the  oil  varies  from  about 
13°  to  17 J°  B.,  the  average  for  the  area  probably  being  about  16°. 

ZIER-PORTER  AND  SCRIBNER-M.  K.  & T.  AREA. 

LOCATION. 

This  area  comprises  the  southern  part  of  sec.  1,  T.  20  S.,  R.  14  E., 
the  southern  part  of  the  Esperanza  property,  sec.  6,  T.  20  S.,  R.  15  E., 
and  the  regions  in  sec.  12,  T.  20  S.,  R.  14  E.,  and  secs.  7 and  8,  T.  20  S., 
R.  15  E.  The  companies  operating  in  this  area  are  the  Zier,  Ward, 
Seneca,  Cypress,  Pennsylvania-Coalinga,  Esperanza,  Shawmut,  Sec- 
tion Seven,  Coalinga  Pacific,  Porter  and  Scribner,  Brix  and  Buntin 
(B.  & B.),  California  and  New  York,  and  M.  K.  & T.  The  wells  are 
located  on  the  flanks  of  the  southeast-dipping  monocline  which 
governs  the  structure  in  the  Westside  field. 

GEOLOGY  OF  THE  WELLS. 

The  wells  start  down  in  the  basal  Etchegoin  or  the  immediately 
underlying  soft  beds  of  the  Jacalitos  formation.  Zone  B,  the  one 
shown  in  contour  on  the  map  (PI.  II),  is  at  present  the  most  important 


94 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


zone  in  this  part  of  the  field,  and  yields  the  greater  part  of  the  produc- 
tion. In  the  western  part  of  the  area  it  varies  from  alternating  sands 
and  shales  to  a single  bed  of  coarse  sand  25  feet  thick.  The  gravity 
of  the  oil  from  the  zone  in  this  part  of  the  area  varies  from  13°  to  14°  B. 
Farther  east  and  lower  down  on  the  dip  the  gravity  of  the  product 
from  zone  B is  considerably  higher,  ranging  from  17°  to  18°  B.  The  . 
beds  yielding  this  lighter  oil  may  possibly  not  be  continuous  with 
those  farther  west  which  produce  the  oil  of  14°  B.  gravity.  On  the 
contrary,  the  sands  yielding  the  latter  may  possibly  be  represented 
in  the  eastern  part  of  the  area  by  the  sands  yielding  14°  B.  oil  which 
immediately  underlie  the  17°  B.  oil  sand.  The  17°  B.  oil  sand  is  not 
fine  grained,  but  is  fairly  coarse  and  in  many  of  the  wells  contains 
shark’s  teeth,  as  it  does  in  the  area  farther  north.  The  zone,  as  indi- 
cated by  logs,  varies  in  thickness  from  7 to  60  feet  in  the  central  part 
of  the  area.  The  production  from  a single  sand  in  this  zone  ranges 
from  40  or  50  barrels  up  to  the  daily  maximum  of  about  200  barrels 
per  well.  The  light-oil  sand  appears  to  be  missing  in  some  of  the 
wells  according  to  their  logs,  but  it  is  believed  that  the  formation  is 
represented  in  the  well,  but  was  overlooked  by  the  driller  while  the 
hole  was  full  of  water.  In  the  deeper  wells,  toward  the  eastern  end 
of  the  area,  zone  B maintains  the  characteristics  just  described,  vary- 
ing in  thickness  from  8 to  30  feet,  apparently  being  mixed  with  some 
shale  in  the  thicker  portion. 

As  in  the  areas  farther  north,  zone  B thickens  rapidly  toward  the 
east  until  in  the  region  of  sec.  8,  T.  20  S.,  R.  15  E.,  indications  of 
petroleum  are  found  throughout  a vertical  distance  of  over  1,100  feet. 
Here  zone  B is  believed  to  be  represented  by  what  is  known  as  the 
third  or  light-oil  sand  of  the  M.  K.  & T.  wells,  which  lies  several  hun- 
dred feet  above  the  most  productive  sands  in  those  holes,  is  medium 
grained,  nearly  100  feet  thick,  and  is  said  to  yield  oil  of  22°  B.  If  zone 
B is  continuous,  wells  located  between  the  Porter  and  Scribner  and 
M.  K.  & T.  leases  ought  to  show  a gradation  in  gravity  from  17°  to  18° 
B.  in  the  former  to  the  22°  B.  oil  in  the  latter,  which  is  much  farther 
down  the  dip.  This  decrease  in  specific  gravity  (increase  in  degrees 
Baume)  down  the  dip  agrees  with  the  mode  of  variation  found  in 
most  instances  in  the  other  California  fields  examined  by  the  writers. 

The  same  tar-sand  zone  (zone  A)  is  encountered  above  zone  B in 
this  area  as  is  found  in  the  same  portion  throughout  most  of  the 
remainder  of  the  Westside  field.  It  varies  in  thickness  from  20  or  30 
feet  to  over  100  feet,  being  exceedingly  irregular  as  reported  in  the 
well  logs,  although  it  is  on  the  whole  believed  to  be  thicker  down  the 
dip  toward  the  east.  The  tar  sands  are  usually  intercalated  with 
shale  and  are  often  dry,  but  in  some  wells  yield  a small  production  of 
heavy  oil  of  about  14°  B.  gravity  or  heavier.  Prominent  sandstone 
shells  are  usually  associated  with  the  sands  and  shales  of  this  zone, 
some  of  these  shells  being  traceable  from  well  to  well,  and  one  in 


THE  OIL  FIELDS. 


95 


particular,  of  considerable  importance,  has  been  called  the  “Big 
Shell.” 

Below  zone  B and  closely  associated  with  it  is  a zone  of  14°  or  15°  B. 
oil.  This  zone  (zone  D)  has  been  penetrated  in  some  of  the  wells  for 
over  300  feet  and  found  to  consist  of  alternating  sands  and  blue  and 
brown  shales,  the  brown  shales  usually  predominating.  It  is  barely 
possible  that  this  lowest  shale  in  the  deepest  wells  is  Tejon  (Eocene), 
but  no  proof  of  this  is  available.  Zone  D is  probably  equivalent  in 
part  to  the  lower  Miocene  sand  of  the  Lucile  well  and  the  wells  in  the 
Eastside  field.  In  the  deepest  wells,  which  obtain  most  of  their  oil 
from  zone  D,  the  latter  is  always  more  productive  than  zone  B. 

Three  or  more  water  sands  are  usually  encountered  in  the  wells  in 
this  area.  In  the  shallower  wells  and  even  in  some  of  the  deeper  ones 
the  water  sand  is  met  at  depths  of  less  than  200  feet.  Below  this 
first  layer  and  separated  from  it  by  about  400  feet  of  shale  is  usually 
the  second  sand,  but  in  some  of  the  wells  within  this  distance  minor 
beds  carrying  water  are  encountered.  Below  the  second  main  water 
sand  and  immediately  overlying  the  tar  zone  (zone  A)  is  a rather 
persistent  stratum  of  sulphur  water  reported  in  most  but  not  all  of 
the  wells.  It  is  more  commonly  found  in  the  deeper  holes  and  may 
be  represented  in  the  wells  toward  the  western  part  of  the  area  and 
higher  up  on  the  dip  by  certain  members  of  the  tar-sand  zone.  If  this 
be  so,  it  is  interesting  as  showing  that  the  hydrocarbons  in  the  tar 
sand  have  been  forced  upward  by  the  sulphur  water  which  fills  up 
this  particular  porous  stratum,  presumably  under  hydrostatic  pres- 


sure. 

Typical  well  log  in  Zier-Porter  and  Scribner- M.  K.  & T.  areas. 

Feet. 

Surface  clay  and  sand  with  a little  gravel 200 

Water  sand 20-  40 

Blue  shale 350 

Water  sand  or  water  gravel 40 

Sulphur  water  sand  (main  sulphur) 30-  50 

Blue  shale  or  shells JO-  20 

Alternating  tar  sands  (zone  A ) and  shale  with  50  or  more  feet  of  shale  and  shell 

at  the  bottom 200 

Productive  17°  or  18°  B.  oil  sand  (zone  B) 10-  60 

Alternating  oil  sands  and  blue  and  brown  shales,  including  zone  D 300 


PRODUCT.. 

The  production  of  the  individual  wells  in  this  area  varies  from  40 
or  50  barrels  to  a maximum  of  about  300  barrels  per  day.  The  gravity 
of  the  oil  in  those  wells  in  the  western  part  of  the  area,  well  up  on  the 
dip,  is  about  12°  to  14°  B.,  while  in  the  deeper  wells,  producing  from 
the  light-oil  sand,  an  average  of  about  17°  or  18°  B.  oil  is  obtained. 
The  deepest  well  in  the  area,  the  M.  K.  & T.,  is  said  to  yield  oil  of 
about  16J°  B.  This  oil  is  believed  to  come  from  zone  P*  in  the 
Vaqueros  (lower  Miocene)  formation. 


96 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


ASSOCIATED -CALEDONIAN-UNION  AREA. 

LOCATION. 

The  area  described  under  this  heading  embraces  the  region  from 
the  Union  lease  in  sec.  13,  T.  20  S.,  R.  14  E.,  southward  to  the  southern 
part  of  sec.  36  in  the  same  township  and  range.  It  includes  well  No. 

5 and  all  other  Associated  wells  farther  north  in  sec.  36;  also  the 
properties  of  the  Kern  Trading  and  Oil,  Southern  Pacific  Railroad, 
Valley  Slope,  Cawder,  Blue  Diamond,  Caledonian,  Angelus,  Ozark, 
Euclid,  Marengo,  Traders,  Norse,  Premier,  Claremont,  Wabash,  Inca, 
St.  Paul-Fresno,  Coalinga  Western,  New  Home,  M.  M.  Kew,  Sleep 

6 Fitzgerald,  Coalinga  Banner,  Coalinga  Petroleum,  Elgar  Adams, 
and  Union  oil  companies. 

STRUCTURE. 

The  wells  in  this  area  are  located  on  the  east-dipping  monocline  of 
the  Westside  field,  the  southern  part  of  the  area  being  located  near 
the  point  where  the  strike  of  the  beds  changes  from  south  to  east  of 
south.  Except  for  a local  flexure,  which  is  possibly  the  continuation 
of  one  of  the  lines  of  disturbance  in  the  White  Creek  syncline,  the 
general  position  of  the  beds  is  regular  and  they  have  an  easterly  dip 
of  11°  to  22°.  The  beds  apparently  flatten  out  in  passing  east  from 
the  steeper  hills  in  the  western  and  southwestern  parts  of  the  area 
to  the  valley  floor. 

GEOLOGY  OF  THE  WELLS. 

The  wells  start  down  in  the  soft  beds  of  the  Etchegoin  formation  or 
of  the  immediately  underlying  Jacalitos  formation.  Zone  B,  shown 
in  contour  on  the  map  (PI.  II),  is  the  principal  productive  zone  in  this 
field,  as  in  those  farther  north.  In  the  northern  part  of  the  area  the 
zone  consists  usually  of  a single  medium  to  coarse  grained  sand, 
varying  in  thickness  from  20  to  30  feet.  This  thickness  is  fairly 
uniform  throughout  the  northern  part  of  the  area,  except  that  por- 
tion well  down  on  the  dip,  where  the  zone  apparent^  thickens  and  is 
penetrated  for  nearly  40  feet  in  some  of  the  wells.  It  also  thickens 
locally  toward  the  western  edge  of  the  area,  50  feet  of  productive  sand 
being  recorded  in  one  of  the  shallower  wells.  It  is  believed,  however, 
that  in  this  well  a part  of  the  thickness  is  made  up  of  intercalated 
shale. 

Southward  the  sand  apparently  becomes  less  and  less  productive, 
the  southernmost  well  so  far  drilled  which  is  believed  to  obtain  oil 
in  commercial  quantities  from  this  zone  being  Associated  No.  5. 
Here  the  productive  sand  is  practically  of  the  same,  thickness  as  the 
average  farther  north,  but  in  the  wells  still  farther  south  the  produc- 
tive sand  pinches  out  or  is  practically  dry.  The  gravity  of  the  oil 


THE  OIL  FIELDS. 


97 


varies  from  13°  to  17°  B.,  apparently  being  heavier  toward  the  outcrop 
of  the  beds  and  lighter  down  the  dip.  A variation  in  gravity  between 
14°  to  15°  along  the  strike  is  also  noticeable,  the  southernmost  wells 
producing  the  lighter  oil. 

Although  zone  B is  the  first  productive  zone  encountered  in  the 
wells,  there  is  above  it  a tar  sand  called  the  “ Big  Gumbo,”  which 
is  penetrated  by  nearly  all  the  wells  from  the  Union  south  to  the  line 
of  Associated  wells  along  the  northern  side  of  sec:  36.  This  gumbo 
sand,  as  the  name  implies,  carries  a heavy  oil  or  tar,  which  has  so  far 
not  been  utilized  in  any  of  the  wells.  In  the  region  of  the  Caledonian 
wells  at  the  western  edge  of  the  developed  territory  and  farther  up  on 
the  dip  there  is  still  a higher  oil  sand,  but  this  also  is  nonproductive. 

Below  zone  B are  three  well-defined  oil  sands  throughout  the 
region  from  the  Union  wells  southward  as  far  at  least  as  the  north 
edge  of  sec.  36.  The  uppermost  of  these  sands  varies  from  10  to  50 
feet  in  thickness,  while  the  second  is  usually  somewhat  thinner. 
Hard  shells  are  often  associated  with  these  lower  sands,  but  in  many 
of  the  wells  blue  shale  is  apparently  the  only  parting.  In  some 
instances  the  sands  below  zone  B are  divided  into  three  or  four  minor 
layers  which  show  little  regularity  in  thickness  between  the  different 
wells. 

The  gravity  of  the  oil  in  the  zone  below  zone  B is  usually  about  the 
same  as  that  in  zone  B,  but  in  the  Caledonian  and  Angelus  regions  an 
oil  sand  carrying  17°  B.  petroleum  is  found  immediately  underlying 
zone  B.  It  is  barely  possible  that  this  may  be  the  equivalent  of  the 
light-oil  sand  in  the  region  of  the  Coalinga  Pacific  and  other  wells  of 
that  same  area,  but  it  is  the  opinion  of  the  writers  that  there  is  no 
direct  connection  between  beds  carrying  the  light  oil  in  this  southern 
part  and  the  beds  carrying  oil  of  the  same  gravity  in  the  region  north 
of  Los  Gatos  Creek. 

In  the  region  of  the  Wabash  and  Inca  properties  the  oil  sands  are 
apparently  the  most  regular  of  the  Westside  field,  but  on  each  side  of 
this  particularly  regular  zone  the  variations  in  the  sands  is  consider- 
able from  well  to  well,  both  along  and  across  the  strike  of  the  beds. 

A persistent  stratum  of  sulphur  water  sand  is  encountered  in  most 
of  the  wells  between  the  gumbo  or  tar  sand  and  zone  B.  This 
sulphur  sand  varies  in  thickness  from  about  10  to  20  feet,  although  in 
one  of  the  Wabash  wells  it  has  apparently  split  up  into  two  sands 
separated  by  shale,  each  sand  member  being  somewhat  less  than  10 
feet  in  thickness.  In  certain  wells  of  this  area  the  sulphur  sand 
contains  traces  of  oil,  especially  in  those  wells  along  the  north  side  of 
sec.  36  and  in  some  of  the  Union  wells. 

The  formations  above  the  zone  of  the  gumbo  or  tar  sand  usually 
contain  two  or  more  water  sands.  In  most  of  the  wells  the  first  sand 
52332— Bull.  357—03 7 


98 


COALINGA  OIL  DISTKICT,  CALIFOKNIA. 


is  encountered  at  depths  under  200  feet,  but  between  this  sand  and 
the  gumbo  the  occurrence  of  water  is  irregular.  In  some  of  the  wells 
water  sand  approximating  50  feet  in  thickness  is  encountered  200 
feet  below  the  first  water  sand,  whereas  in  wells  near  by  the  second 
water  sand  may  be  only  10  feet  thick  and  may  be  separated  from  the 
first  sand  by  one  or  two  other  strata  carrying  water.  The  water  from 
all  of  those  sands  is  considerably  mineralized  and  is  not  fit  for  domestic 
uses. 


Typical  well  log  in  Associated- Caledonian- Union  area. 

Shale : , 

Water  sand 

Shale  with  some  dry  sand  or  gravel . 

Water  sand 

Blue  shale  with  some  dry  sands  and  occasionally  some  water  sand 

Tar  zone,  zone  A 

Blue  shale 

Sulphur- water  sand 

Blue  shale  with  occasionally  fine  sand  layers.  (The  water  is  generally  shut 
off  in  the  upper  part  of  this  shale  zone.  Such  a proceeding  is  doubtless 
flooding  the  gumbo  sand,  but  as  this  tar  sand  is  not  believed  to  be  produc- 
tive in  any  part  of  the  field  the  flooding  is  doing  no  harm.) 

Zone  B and  various  oil  sands  of  more  or  less  importance,  the  whole  being  thin- 
nest near  the  outcrop  and  thickening  gradually  down  the  dip 


Feet. 
150 
20-30 
200 
20-  50 
600 
8-  50 
20-100 
20 


100-200 

100-225 


One  of  the  Caledonian  wells  was  drilled  to  a depth  of  over  2,300 
feet,  but  from  the  depth  of  something  over  700  feet  it  passed  through 
the  Usually  unproductive  Eocene  brown  and  blue  shales  (Tejon  for- 
mation) yielding  warm  salt  water  of  110°  F.  near  the  bottom.  Sul- 
phur water  was  also  encountered  at  about  1,600  feet  in  this  well,  and 
a little  greenish  oil  of  over  17°  gravity  was  encountered  near  the  1,000- 
foot  mark.  The  base  of  the  productive  measure  in  this  area  is  believed 
to  be  marked  by  a persistent  stratum  of  salt  or  brackish  water,  which 
is  encountered  in  wells  drilled  into  the  underlying  Tejon  shales. 


PRODUCT. 


The  product  in  the  wells  so  far  drilled  in  this  area  comes  from  zone 
B,  the  Jacalitos  (upper  Miocene)  formation.  The  daily  production 
of  the  individual  wells  varies  from  about  400  barrels  in  the  deeper 
wells  to  50  or  60  barrels  in  the  shallower.  Many  of  the  wells  flow  at 
first,  and  some  of  the  deeper  ones  continue  to  flow  for  two  or  three 
years,  but  most  of  the  wells  are  pumped  after  the  initial  head  of  gas 
has  blown  off.  Much  sand  accompanies  the  oil,  especially  in  the 
shallower  wells,  running  as  high  as  50  per  cent  at  first  in  some  of  the 
wells.  Large  amounts  of  gas  are  produced  by  most  of  the  wells. 
The  gravity  of  the  oil  varies  from  12°  B.  in  the  shallow  wells,  those  up 
on  the  dip,  to  17°  for  the  deeper  holes.  Three  sands  are  recognized 
in  the  productive  zone,  the  upper  one  yielding  the  lightest  oil. 


THE  OIL  FIELDS. 


99 


AREA  BETWEEN  WALTHAM  CREEK  AND  SAN  JOAQUIN  VALLEY  COAL  MINE. 

LOCATION. 

The  area  treated  in  the  following  paragraphs  comprises  the  terri- 
tory lying  between  the  Cretaceous-Vaqueros  (lower  Miocene)  contact 
(which  extends  northwestward  from  Alcalde)  and  the  valley  floor 
west  of  Coalinga,  and  between  Waltham  Creek  and  the  reigon  of  the 
San  Joaquin  Valley  coal  mine  in  the  NW.  £ sec.  26,  T.  20  S.,  R.  14  E. 
A portion  of  this  region,  however,  that  in  which  the  wells  of  the  Sunny- 
side  and  Westlake-Rommel  oil  companies  are  situated,  is  omitted  and 
will  be  considered  separately. 

The  oil  companies  operating  within  this  region  include  the  Mount 
Hamilton,  Commercial  Petroleum,  West  Coalinga,  Coalinga  Zenith, 
Summit,  Z.  L.  Phelps,  Blaine,  Yellowstone,  Coalinga  Southern,  Sec- 
tion Six,  T.  C.,  Lucile,  Shreeve,  St.  Francis,  Associated,  Southern 
Pacific  Railroad,  and  some  others  not  yet  prosecuting  development 
work. 

GEOLOGY. 

The  formations  involved  in  the  geology  of  this  area  comprise  the 
Knoxville-Chico  (Cretaceous,  sandstone  and  shale),  the  Tejon 
(Eocene,  sandstone  and  shale),  a series  of  sandstones  overlain  by 
soft  shale  which  are  believed  to  be  largely  of  Vaqueros  (lower  Miocene) 
age,  the  Jacalitos  (early  upper  Miocene,  sandstone,  conglomerate, 
and  shale),  and  the  Etchegoin  (late  upper  Miocene,  sand  and  clay 
shale). 

The  Knoxville-Chico  rocks  (Cretaceous)  consist  of  dark  thin-bedded 
shale  with  some  sandstone,  the  latter  in  places  carrying  the  character- 
istic brown  concretions.  It  outcrops  west  of  the  area  under  discussion 
and  extends  in  a northwesterly  direction  into  the  hills  south  of  Los 
Gatos  Creek.  In  the  main  the  Cretaceous  beds  are  steeply  tilted, 
forming  a monocline  with  an  approximate  dip  of  60°  SE.  They  carry 
no  oil  in  commercial  quantities,  but  are  believed  to  yield  the  water  in 
the  Henshaw  and  West  Coalinga  wells. 

The  Tejon  (Eocene)  formation  consists  largely  of  medium-grained 
sandstone  with  some  intercalated  shales  at  the  base  and  a consider- 
able thickness  of  shale  at  the  top.  It  occupies  a small  area  in  the 
SW.  I sec.  26,  T.  20  S.,  R.  14  E.,  just  south  of  the  San  Joaquin 
Valley  coal  mine.  With  the  exception  of  this  small  outcrop  the  Tejon 
in  this  area  is  entirely  covered  by  the  later  beds,  which  overlap  it 
from  the  east  and  south.  The  basal  Tejon  overlies  the  Cretaceous 
apparently  conformably  and  dips  northeastward  at  an  angle  of  about 
30°  and  is  itself  in  turn  overlain  unconformably  by  the  Miocene  beds. 

Unconformably  overlying  the  Knoxville-Chico  (Cretaceous)  and 
the  Tejon  (Eocene)  just  described  is  a series  of  beds  consisting  of 
about  250  feet  of  sandstones  and  over  100  feet  of  soft  dark-blue  shale. 


100  COALING  A OIL  DISTRICT,  CALIFORNIA. 

These  beds  are  known  to  be  Vaqueros  at  the  base,  but  the  age  of  the 
uppermost  member,  the  shale,  is  unknown.  The  latter,  however, 
may  possibly  be  the  equivalent  of  the  “Big  Blue”  in  the  northern  end 
of  the  Coalinga  field,  although  in  the  area  under  discussion  it  has  been 
mapped  with  the  Vaqueros,  and  in  the  Eastside  field  it  is  included  in 
the  Santa  Margarita.  The  basal  sandstone  of  the  Vaqueros  formation 
may  be  traced  from  a short  distance  south  of  the  San  Joaquin  Valley 
coal  mine  southward  across  the  northwest  corner  of  sec.  35,  T.  20  S., 
R.  14  E.,  along  the  western  edge  of  the  same  section,  into  the  middle 
of  the  NW.  1 sec.  2,  T.  21  S.,  R.  14  E.,  thence  southeasterly  to  the 
bottom  of  the  canyon  near  the  middle  of  the  south  line  of  the  SE.  J 
sec*.  2.  Thence  it  passes  westward  below  and  north  of  the  summit 
of  the  big  ridge  which  extends  several  miles  northwesterly  from 
Alcalde.  Near  the  San  Joaquin  Valley  coal  mine  the  Vaqueros  over- 
lies  the  Tejon  (Eocene),  but  near  the  northwest  corner  of  sec.  35  it 
crosses  the  contact  between  the  Knoxville-Chico  (Cretaceous)  and 
the  Tejon,  and  from  there  south  westward  it  overlies  the  Knoxville- 
Chico.  The  contact  between  the  Knoxville-Chico  and  the  Tejon  is 
believed  to  extend  southeasterly  underneath  the  Vaqueros  diagonally 
through  sec.  35,  T.  20  S.,  R.  14  E.,  and  diagonally  through  sec.  1, 
T.  21  S.,  R.  14  E.  Its  course  from  the  latter  region  is  not  definitely 
known,  but  can  be  surmised,  as  is  stated  elsewhere  (p.  118).  The 
tracing  of  this  contact  beneath  the  Vaqueros  is  important  because  of 
the  fact  that  the  oil  is  derived  from  the  Eocene  shale,  and  it  is 
believed  that  wherever  the  Vaqueros  or  other  formations  overlie  the 
Tejon  they  will  be  found  more  or  less  petroliferous,  while  in  the 
areas  where  the  same  formations  overlie  the  Knoxville-Chico  they  will 
be  found  barren  or  containing  only  such  petroleum  as  has  migrated 
along  the  strata  from  areas  underlain  by  the  Tejon.  It  is  worthy  of 
note  in  this  connection  that  along  practically  the  whole  extent  of  the 
outcrop  of  the  base  of  the  Vaqueros  from  the  San  Joaquin  Valley  coal 
mine  southward  to  the  southern  part  of  sec.  2,  T.  21  S.,  R.  14  E.,  the 
basal  beds  are  more  or  less  petroliferous.  The  indications  are  so 
strong  in  certain  places,  notably  in  the  SE.  J sec.  2,  that  tunnels  have 
been  run  into  the  base  of  the  Vaqueros  sands  with  the  expectation  of 
obtaining  petroleum  in  commercial  quantities. 

Westward  from  the  southeastern  part  of  sec.  2 the  basal  Vaqueros 
sands  become  less  and  less  petroliferous  until  on  the  flanks  of  the 
ridge  spoken  of  as  extending  northwestward  from  Alcalde  the  beds 
show  no  indications  of  petroleum. 

The  description  of  the  geologic  section  exposed  on  the  surface  along 
a line  extending  from  the  middle  of  the  southern  line  of  sec.  2,  T.  21  S.,- 
R.  14  E.,  in  Anticline  Canyon,  to  the  top  of  Flag  Hill  (located  in  the 
SE.  I sec.  1,  T.  21  S.,  R.  14  E.,  and  shown  as  the  triangulation  station 


THE  OIL  FIELDS. 


101 


on  the  topographic  map)  and  thence  in  a direct  line  to  the  Lucile  well 
covers  all  the  formations  of  the  area  under  discussion;  this  section  is 
based  upon  a detailed  surface  traverse  and  in  a general  way  upon  the 
well  logs  of  secs.  6 and  36  to  the  northeast: 

Geologic  section  from  Anticline  Canyon  in  S.  % SE.  \ sec.  2 , T.  21  S.,  R.  14  E.,  to  Lucile 
well  ( beginning  with  lower  strata). 

[Dip  approximately  20°  NE.] 

Vaqueros  (lower  Miocene).  Beds  1-4. 

Bed  1.  Much-discolored  and  rusty-yellowish  sand  and  soft  sandstone,  highly 
charged  with  petroleum  in  the  immediate  vicinity  of  Anticline  Canyon,  and 
about  150  feet  thick.  Not  yet  pierced  by  any  of  the  wells  in  the  sec.  6 area,  but 
is  believed  to  be  a rich  oil-bearing  sand  throughout  its  entire  thickness.  Repre- 
sents the  basal  part  of  zone  D of  the  developed  territory. 

Bed  2.  Largely  gypsiferous  sand,  with  a hard  fossiliferous  layer  at  base.  The 
fossils,  which  occur  abundantly  in  Anticline  Canyon  a short  distance  below  the 
southern  line  of  section  2,  are  believed  to  be  from  the  same  bed  as  the  fossil 
“clam”  shells  thrown  out  in  the  sand  from  the  bottom  of  Lucile  well  No.  1. 
About  150  feet  thick;  probably  represents  parts  of  zones  C and  D in  the  Eastside 
field. 

Bed  3.  Soft  sand  with  pebbly  layers  and  occasional  hard,  coarse,  rusty,  sandstone 
strata,  which  would  be  called  “sandstone  shell”  if  encountered  in  the  wells. 
About  200  feet  thick,  and  is  also  a part  of  zones  C and  D.  Beds  2 and  3 appar- 
ently thin  out  slightly  toward  the  valley,  as  the  thickness  disclosed  by  the  well 
logs  is  somewhat  less  than  that  obtained  by  calculation  from  the  surface 
outcrops. 

Bed  4.  Largely  clay,  about  250  feet  thick,  and  may  be  the  equivalent  of  the  “ Big 
Blue”  in  the  Eastside  field. 

Jacalitos  (early  upper  Miocene).  Beds  5-11. 

Bed  5.  Largely  pebbly  sand  overlain  by  thin-bedded  sand  and  soft  sandstone. 
Bed  of  fossils,  largely  Zirphsea.  at  top;  believed  to  be  the  ones  reported  in  both 
the  Shreeve  and  Lucile  logs.  These  are  an  important  tie  line,  not  only  in  this 
particular  area,  but  also  throughout  the  Coalinga  district.  Bed  believed  to  be 
the  same  as  that  which  rests  upon  or  near  the  Tejon,  west  of  that  part  of  the 
Westside  field  lying  north  of  the  San  Joaquin  Valley  coal  mine,  and  believed 
to  be  of  upper  Miocene  age.  Zone  B , in  the  wells  of  the  south  and  central  parts 
of  the  Westside  field,  is  between  100  and  200  feet  in  thickness. 

Bed  6.  Above  the  fossil  bed  are  some  coarse  gray  sand  layers.  Well  in  the  NE.  \ 
SW.  I sec.  12,  T.  21  S.,  R.  14  E.,  begins  in  this  zone  of  sand. 

Bed  7.  Clay;  apparently  thickens  somewhat  toward  the  valley,  especially  between 
the  Shreeve  and  Lucile  wells. 

Bed  8.  Persistent  layer  of  soft  pebbly  sandstone,  recognized  in  both  the  Shreeve 
and  Lucile  well  logs. 

Bed  9.  Ten-foot  layer  of  clay. 

Bed  10.  Another  pebbly  sandstone  layer,  apparently  not  so  persistent  as  bed  8. 

Bed  11.  Important  and  widespread  soft  blue  clay. 

Etchegoin  (uppermost  Miocene).  Beds  12-17. 

Bed  12.  Brown  sand  at  the  base,  10  feet  of  hard  sandstone,  then  a layer  of  sand, 
another  layer  of  sandstone,  and  finally  soft  sandstone  at  the  top. 

Bed  13.  Soft  blue  shale,  15  to  200  feet  thick. 


102 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Etchegoin  (uppermost  Miocene).  Beds  12-17 — Continued. 

Bed  14.  Coarse  brown  to  greenish  pebbly  sand  at  base,  overlain  by  coarse 
brown  sand,  containing  numerous  large  fossil  sand  dollars,  Echinarachnius  gibbsi 
Remond.  About  125  feet  thick. 

Bed  15.  This  is  sand  and  soft  sandstone,  pebbly  at  the  bottom,  and  contains 
numerous  fossils.  It  is  known  as  a fossil  bed  in  the  wells  in  some  parts  of  the 
field  and  contains  such  species  as  Pecten  oweni  Arnold,  Glycymeris,  etc.  It  is  the 
Glycymeris  zone  not  far  above  the  base  of  the  Etchegoin  formation. 

Bed  16.  This  layer  is  of  bluish  clay,  about  100  feet  thick. 

Bed  17.  From  the  top  of  bed  17  down  to  the  detritus-covered  valley  floor  in  the 
vicinity  of  Lucile  well  No.  1 the  beds  exposed  are  largely  coarse  sands  with 
occasional  pebbly  layers.  Toward  the  edge  of  the  hills  some  of  the  beds  contain 
cobbles  of  considerable  size  and  fossils  indicating  the  same  horizon  as  the 
Pecten  coaling aensis  zone,  frequently  mentioned  in  the  discussion  of  the  geology 
as  near  the  top  of  the  Etchegoin.  Usually  spoken  of  by  the  drillers  as  surface 
formation,  as  they  appear  to  be  largely  incoherent  and  of  a heterogeneous  char- 
acter. Uppermost  possibly  represent  part  of  the  Paso  Robles  formation. 

STRUCTURE. 

The  main  structural  feature  is,  of  course,  the  great  southeastward 
dipping  monocline  that  extends  from  the  top  of  Curry  Mountain  and 
Juniper  Ridge  to  the  middle  of  Pleasant  Valley.  There  are,  how- 
ever, one  or  two  local  lines  of  disturbance  within  the  area  which  are 
worthy  of  mention.  The  most  important  begins  in  the  Knoxville- 
Chico  rocks  (Cretaceous)  somewhere  northwest  of  sec.  2,  T.  21  S., 
R.  14  E.,  and  passes  southeastward  apparently  almost  coincident 
with  the  . bed  of  Anticline  Canyon.  From  the  south  line  of  sec.  2 
to  the  middle  of  the  E.  \ SW.  J sec.  12  this  line  of  disturbance  has 
the  character  of  a southeastward-plunging  anticline.  The  dips  on 
the  east  are  apparently  about  20°,  while  those  toward  the  south  vary 
from  8°  or  10°  in  the  region  immediately  south  of  sec.  2 to  30°  or  40° 
in  the  southern  part  of  the  SW.  J sec.  12.  At  a point  a short  distance 
west  of  the  east  line  of  the  SW.  J sec.  12  the  line  of  disturbance  bends 
abruptly  and  passes  almost  due  east  for  nearly  three-fourths  of  a mile. 
Along  the  east-west  portion  the  disturbance  takes  the  form  of  a fault, 
although  the  beds  in  a general  way  dip  away  on  both  sides  of  the 
fault  line.  The  line  of  fracture  may  be  traced  from  the  dome  of  the 
anticline  in  the  eastern  wall  of  Anticline  Canyon,  in  the  eastern  part 
of  the  SW.  i sec.  12,  to  a point  less  than  one-fourth  mile  northeast 
of  the  Commercial  Petroleum  Company’s  well  No.  1 in  the  SE.  £ sec. 
12.  The  beds  on  the  southern  side  of  the  fault  are  inclined  in  a 
southerly  direction  with  the  dips  varying  from  60°  or  70°  near  the 
fracture  to  35°  or  40°  some  distance  south  of  it.  North  of  the  fracture 
the  beds  dip  about  20°  NE.  and  abut  sharply  against  the  steep  south- 
dipping beds.  From  the  eastern  line  of  the  SE.  J sec.  12  the  line  of 
fracture  apparently  bends  abruptly  toward  the  southeast  and  dies 
out  beneath  the  superficial  deposits  of  Alcalde  Canyon. 


THE  OIL  FIELDS. 


103 


A minor  disturbance,  probably  intimately  connected  with  the  one 
just  described,  is  developed  in  an  east-west  ridge  in  the  NE.  \ sec.  7, 
T.  21  S.,  R.  15  E.  An  examination  of  the  surface  geology  of  this 
region,  beginning  at  the  railroad  cut  in  the  NW.  J sec.  8,  T.  21  S., 

R.  15  E.,  discloses,  first,  coarse  sandstone  beds  dipping  N,  35°  E., 
at  angles  of  10°  to  50°;  westward  from  here  along  the  crest  of  the 
ridge  dips  of  N.  25°  W.  16°  are  encountered;  then  dips  of  20°  a little 
farther  toward  the  west,  and  finally,  where  the  strike  of  the  bed 
swings  around  toward  the  northwest,  dips  as  high  as  40°.  Northwest 
from  this  maximum  dip  the  beds  drop  to  30°  northeast  and  finally  to 
the  prevailing  dip  of  18°  to  20°  along  the  western  side  of  sec.  6. 

A third  line  of  disturbance  is  visible  in  the  small  bluff  on  the  north- 
west side  of  Alcalde  Canyon  immediately  north  of  Alcalde  station. 
This  is  a sharp  anticlinal  fold  in  gray  and  brown  shale  with  a dip  of 
20°  S.  53°  W.  on  the  one  side,  and  of  70°  N.  55°  E.  on  the  other. 
Mount  Hamilton  well  No.  1 is  drilled  practically  on  the  axis  of  this 
* anticline  less  than  one-fourth  mile  from  the  bluff  mentioned.  An 
examination  of  the  territory  northwest  of  the  Mount  Hamilton  well, 
embracing:  the  territory  along:  the  contact  between  the  Knoxville- 
Chico  and  the  Tejon,  discloses  dips  that  apparently  indicate  a north- 
westward continuation  of  the  anticline  as  far  as  the  SE.  \ sec.  10, 
T.  21  S.,  R.  14  E.  The  beds  in  this  region  are  lying  so  nearly  hori- 
zontal and  have  been  so  affected  by  landslides  that  it  is  impossible 
to  determine  definitely  the  course  of  the  line  of  disturbance.  This 
structural  feature,  however,  has  no  apparent  influence  whatever 
upon  the  oil-bearing  beds,  but  is  described  simply  to  indicate  the 
localization  of  the  forces  producing  folding  in  the  beds. 

Still  a fourth  line  of  disturbance  enters  the  area  under  discussion 
in  the  southwestern  part  of  sec.  7,  T.  21  S.,  R.  15  E.  This  is  a syn- 
cline which  is  prominently  developed  farther  south  and  has  been 
described  in  the  discussion  of  the  area  south  of  Waltham  Creek  (p.  66). 
In  the  southwest  corner  of  sec.  7 this  syncline  produces  dips  of  40° 

S.  20°  W.,  while  a short  distance  south  the.same  bed  dips  30°  nearly 
due  east,  a little  farther  south  25°  in  the  same  direction,  and  still 
farther  south  20°.  This  syncline  is  apparently  associated  with  the 
Anticline  Canyon  flexure,  but  the  relations  between  the  two  are 
obscured  at  the  critical  point  along  the  south  line  of  sec.  7 by  the 
detrital  material  of  Waltham  Creek. 

In  connection  with  the  folding  and  faulting  which  has  taken  place 
in  sec.  12  it  might  be  well  to  amplify  the  description  of  the 
geology  in  the  vicinity  of  the  Commercial  Petroleum  well  No.  1 in 
the  southeast  corner  of  the  SE.  I sec.  12,  T.  21  S.,  R.  14  E.  A 
section  along  the  surface  of  the  ridge  northward  from  this  well 


104  COALINGA  OIL  DISTRICT,  CALIFORNIA. 

shows  the  following  strata,  all  dipping  approximately  due  south 
about  60°: 

Section  in  Miocene  north  from  Commercial  Petroleum  Company's  well  No.  1,  sec.  12 , 

T.  21  S.,  R.  14  E. 

Feet. 


Soft  sand,  to 30 

Pebbly  sand 40 

Soft  sand 180 

Coarse  sand  with  hard  dark  layers  (“shells”) 240 

Fine  pebbly  sand  (dipping  due  south  60°) 255 

Alternating  coarse  sandstone  and  pebbly  sandstone  beds  with  a particularly  hard 

brown  sand  layer  at  the  base 320 

Soft  blue  shale  and  sandy  shale 620 

Coarse  pebbly  sand,  the  last  half  hard  and  containing  silicified  wood  fragments 

(dip  is  50°  south) 710 

Gray  sand  with  one  or  two  hard  streaks 760 

Soft  blue  gypsiferous  shale 790 

Medium  to  coarse  gray  sandstone 820 


At  820  feet  is  the  fault  line  extending  in  a direction  S.  80°  E.  The  * 
downthrow  is  on  the  north  and  is  probably  ‘at  least  200  feet.  The 
beds  along  the  trace  of  the  fault  are  of  a purplish  and  pink  tint,  this 
discoloration  probably  being  due  to  petroleum  which  has  seeped  up 
along  the  fault.  A comparison  of  the  above  surface  section  and  the 
log  of  the  Commercial  Petroleum  well  indicates  the  reason  for  the  dis- 
crepancy between  this  well  log  and  those  of  the  wells  in  the  sec.  6 
area.  In  the  Commercial  Petroleum  well  the  beds  penetrated  dip 
about  60°,  while  in  the  sec.  6 area  the  beds  dip  less  than  20°.  The 
water  which  occurs  in  the  Commercial  Petroleum  well  is  probably  of 
local  extent  and  is  to  be  associated  with  the  fault  line  which  apparently 
is  cut  by  the  well  near  the  latter’s  junction  with  the  oil  sand.  It  is 
the  belief  of  the  writers  that  it  would  be  impossible  to  put  down  wells 
in  this  faulted  area  and  obtain  the  same  or  even  approximate  results 
in  any  two.  The  region  about  the  corners  of  secs.  12  and  13,  T.  21  S., 
R.  14  E.,  and  secs.  7 and  18,  T.  21  S.,  R.  15  E.,  is  the  center  of  a num- 
ber of  complex  disturbances,  which,  it  is  believed,  have  locally  so  com- 
plicated the  underground  geology  as  to  make  the  exploitation  of  the 
oil  sands  difficult  if  not  impossible. 

GEOLOGY  OF  THE  WELLS. 

The  wells  of  this  area  lie  for  the  most  part  in  the  angle  where  the 
formations  bend  from  a strike  of  south  and  southeast  to  a strike  of 
east  or  east-southeast.  This  change  in  strike  is  caused  by  the  line  of 
disturbance  which  passes  down  Anticline  Canyon  and  bends  abruptly 
east  in  the  SW.  \ sec.  12,  T.  21  S.,  R.  14  E.  The  eastward  continua- 
tion of  this  line  of  disturbance  across  sec.  7,  T.  21  S.,  R.  15  E.,  is  the 
cause  of  the  abrupt  turning  to  the  east  of  all  of  the  formations  on  the 
flanks  of  the  great  monocline  on  the  west  side  of  Pleasant  Valley. 
It  will  be  noticed  by  an  examination  of  the  contour  map  (PI.  II)  that 


THE  OIL  FIELDS. 


105 


the  formations  have  a practically  uniform  dip  of  about  18°  or  20° 
down  to  the  edge  of  the  more  pronounced  hills.  At  the  edge  of  the 
hills  the  dip  flattens  out  to  an  angle  of  about  5°  or  6°.  It  should 
be  observed  in  this  connection  that  the  topography  in  a general 
way  reflects  this  change  in  dip.  This  is  an  important  item  to  remem- 
ber, as  in  other  parts  of  the  field  where  there  are  no  wells  and  in  which 
surface  outcrops  are  lacking  it  may  be  possible  to  judge  in  a general 
way  of  the  position  of  the  underground  formations  by  a critical  exam- 
ination of  the  topography  of  the  region  under  observation.  As  a 
result  of  the  bowing  of  the  strata  the  dips  are  apparently  steepest  in 
sec.  36,  but  flatten  out  and  become  more  regular  north  of  this  area. 
In  the  southern  part  of  sec.  6 and  also  the  northern  part  of  sec.  7 the 
dips  are  very  steep  at  the  surface  outcrop.  The  locus  of  the  steep 
dip  apparently  extends  from  the  surface  underground  in  a northerly 
direction  and  has  its  maximum  effect  on  the  oil  sands  in  the  NW.  \ 
sec.  6 and  the  SE.  \ sec.  36.  Details  of  the  change  in  dips  and  strike 
are  indicated  by  contours  on  the  map  (PL  II)  and  will  not  be  discussed 
further  here. 

All  of  the  wells  within  this  area  start  down  in  the  soft  surface 
sands  and  clays,  which,  below  the  uppermost  superficial  stratum, 
are  believed  to  belong  to  the  Etchegoin  or  possibly  the  Paso  Robles 
formation.  Before  reaching  the  uppermost  oil  zone  (zone  B),  the 
wells  pass  through  four  or  five  well-defined  zones  of  sandstone  with 
as  many  interbedded  layers  of  soft  blue  shale.  Many  of  the  sands 
carry  pebbles  up  to  the  size  of  a marble,  and  some  of  the  blue  shales 
are  also  pebbly.  Water  sands  are  encountered  at  various  depths, 
some  of  them  producing  large  quantities  of  more  or  less  mineralized 
water.  The  Lucile  well  No.  1 and  the  West  Coalinga  well  No.  1 pro- 
duce a great  deal  of  water,  but  from  entirely  different  rocks,  the 
first  from  the  Jacalitos  (upper  Miocene)  the  latter  probably  from  the 
Knoxville-Chico  (Cretaceous).  Some  very  hard  sandstone  shell 
layers  are  encountered  in  the  wells  and  in  one  or  two  places  these 
appear  to  be  rather  persistent  laterally.  The  hard  layer  reported  as 
the  “Big  Shell”  in  some  of  the  wells  is  apparently  not  the  stratum 
so  designated  in  others. 

The  first  oil  zone  (zone  B)  varies  in  thickness  from  about  60  to  150 
feet.  In  some  of  the  wells  it  is  reported  as  nearly  solid  sand,  while  in 
others  it  is  a zone  of  alternating  sandstone  and  shale.  Oil  or  gas,  or 
both,  are  reported  from  it  in  all  of  the  wells  except  Shreeve  No.  1,  but 
it  is  believed  that  indications  of  petroleum  must  have  been  found  in 
this  well  and  overlooked  by  the  driller,  or  else  they  were  not  con- 
sidered of  enough  importance  to  record  in  the  log.  So  far  as  known 
none  of  the  wells  in  this  area  produce  from  this  zone.  The  individual 
sands  of  zone  B vary  from  fine-grained  thin-bedded  layers  intercalated 
with  sandy  shale  to  coarse  conglomeratic  sand  carrying  small  cobbles. 


106 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


As  previously  mentioned,  this  zone  may  be  studied  in  the  east  wall 
of  the  canyon  running  up  to  the  Henshaw  water  well  (SW.  J sec.  35, 
T.  20  S.,  R.  14  E.)  about  half  a mile  southeast  of  this  well. 

Oil  zone  B is  underlain  by  a persistent  stratum  of  mineralized  water, 
either  salt  or  sulphur  or  both,  in  nearly  all  the  wells.  In  some  this 
flow  of  water  was  encountered  at  the  base  of  a hard  sandstone  shell 
underlying  the  oil  strata,  but  in  others  it  is  reported  in  the  lowest  oil 
sand  of  the  zone.  Oil  zone  B is  separated  from  the  lower  or  zone  D by 
between  150  and  200  feet  of  shale  and  shell.  Some  water  sands  and 
tar  sands  are  reported  in  the  space  between  zones  B and  D in  some  of 
the  wells,  but  these  do  not  appear  to  be  very  persistent.  Only  three 
of  the  wells  have  so  far  penetrated  zone  D and  these  touch  only  its 
uppermost  sands.  The  reason  for  this  is  generally  because  the  gas 
pressure  is  great  enough  either  to  make  the  well  flow  or  to  fill  it  up 
with  sand.  The  uppermost  beds  of  zone  D are  fine  grained  and  carry 
oil  of  fairly  light  gravity.  Oil  of  32°  B.  has  been  reported  in  one  of  the 
wells,  and  the  gravity  of  all  the  upper  beds  seems  to  range  from  this 
down  to  26°  B. 

Below  the  zone  of  light  oil  sands  is  a coarser  sand  carrying  fossil 
shells  and  believed  to  be  the  same  as  the  bed  at  the  base  of  bed  2 in 
the  section  on  page  101.  The  oil  from  this  lower  zone  is  much  heavier 
than  that  from  the  upper,  averaging  about  16°  or  17°  B.;  the  pro- 
duction also  is  very  much  greater  from  the  lower  sand  than  from  the 
upper  finer  sands,  and  is,  therefore,  tapped  wherever  possible.  It  is 
the  belief  of  the  writers  that  this  lower  oil  sand  will  furnish  long-lived 
wells,  for  holes  that  simply  tap  its  uppermost  layers  are  very  produc- 
tive and  the  150  or  200  feet  of  sands  that  are  believed  to  underlie  the 
tapped  bed  are  doubtless  heavily  impregnated  with  oil. 

SEC.  2,  T.  21  S.,  R.  14  E.,  AND  VICINITY. 

GEOLOGY  OF  THE  WELLS. 

Underground  conditions  in  the  E.  J sec.  2,  T.  21  S.,  R.  14  E.,  and 
in  the  southern  part  of  sec.  35,  T.  20  S.,  R.  14  E.,  have  been  tested  by 
the  wells  of  the  Sunnyside  Oil  Company  (Henshaw  water  well)  and 
the  Westlake-Rommel  Oil  Company.  The  wells  penetrate  the  north- 
east-dipping beds  of  the  Vaqueros  formation  (lower  Miocene),  which 
overlie  the  steeply  tilted  Knoxville-Chico  (Cretaceous)  strata  exposed 
at  the  surface  toward  the  west.  The  oil  in  this  area  is  believed  to 
have  percolated  along  the  basal  (zone  D)  sands  from  the  east,  where 
these  sands  overlie  the  shales  of  the  Tejon  (Eocene).  Only  four  wells 
have  so  far  been  put  down  in  this  area ; three  were  sunk  several  years 
ago  by  the  Westlake-Rommel  Oil  Company,  and  one  (the  Henshaw 
water  well)  was  put  down  by  Captain  McClurg  for  the  Sunnyside  Oil 
Company  in  1897.  The  logs  of  these  wells  indicate  that  the  petrolif- 
erous zone  is  from  100  feet  to  120  feet  thick  and  consists  of  medium- 
grained sands  interbedded,  especially  toward  the  middle  of  the  zone, 


THE  OIL  FIELDS. 


107 


with  fine  clays  and  harder  sand  layers.  The  sand  carries  a little 
heavy  oil  and  in  the  Westlake-Rommel  wells  is  said  to  have  yielded  no 
gas.  This  lack  of  gas  would  be  expected  in  an  area  so  close  to  the 
outcrop  of  the  oil  sands  where  the  gas  would  have  an  opportunity  to 
escape  from  the  petroliferous  beds.  Water  is  found  associated  with 
the  oil  in  the  uppermost  layer  of  this  zone  in  one  of  the  wells  and  is 
found  abundantly  in  the  sands  just  beneath  the  oil  zone.  In  addition 
to  the  four  wells  mentioned,  tunnels  were  run  in  on  the  outcrop  of 
the  oil  sands  in  the  E.  J sec.  2,  but  did  not  obtain  enough  oil  to  pay 
for  their  operation. 

It  is  believed  that  the  Henshaw  well  obtains  its  water  from  a sand 
in  the  Knoxville-Chico  (Cretaceous),  as  the  depth  at  which  the  sand 
is  penetrated  is  considerably  lower  than  the  base  of  the  Vaqueros 
formation.  As  the  Knoxville-Chico  beds  in  this  region  are  highly 
tilted,  wells  will  be  able  to  tap  the  Henshaw  water  sand  along  a nar- 
row band  only.  As  the  strike  of  the  Knoxville-Chico  is  here  about 
east-northeast,  it  is  believed  that  this  band  strikes  in  a direction  north- 
northwest  or  south-southeast  of  the  Henshaw  well. 

PRODUCT. 

The  daily  yield  of  the  individual  productive  wells  in  the  area 
between  Waltham  Creek  and  the  southern  part  of  sec.  36  ranges  from 
about  100  barrels  in  those  on  the  dip  to  about  800  barrels  in  the 
deeper  holes.  An  initial  production  of  over  1,500  barrels  a day  is 
said  to  have  come  from  one  of  the  wells.  Oil  of  26°  B.  gravity  is 
yielded  by  sands  at  the  top  of  the  lower  zone  (zone  D),  and  as  high 
as  175  barrels  of  oil  a day  is  said  to  have  been  produced  by  one  well 
from  these  sands  alone.  Below  the  light  oil  sands  are  coarser  and 
more  productive  layers  which  yield  the  bulk  of  the  oil  for  this  terri- 
tory. The  gravity  of  the  petroleum  from  this  last  horizon  is  between 
16°  and  17°  B.  The  oil  in  the  light  oil  sands  is  brown;  that  in  the 
zone  of  heavier  oil  is  black. 

KREYENHAGEN  FIELD. 

LOCATION. 

The  region  south  of  -Coalinga  as  far  as  Dudley,  Kings  County, 
including  the  Kettleman  and  Kreyenhagen  Hills  and  Reef  Ridge,  has 
been  known  for  many  years  as  the  Kreyenhagen  oil  district.  For  the 
sake  of  brevity  of  discussion  in  the  present  report  this  territory  has 
been  included  as  a part  of  the  Coalinga  district  and  has  been  divided 
into  two  fields,  the  Kreyenhagen  field  and  the  Kettleman  Hills  field. 
The  area  discussed  as  the  Kreyenhagen  field  lies  on  the  southeastern 
flanks  of  Reef  Ridge  and  extends  from  the  general  region  of  Jacalitos 
Creek  to  Dagany  Gap,  3J  miles  southeast  of  Dudley.  The  area  in 
which  oil  development  has  been  carried  on  constitutes  a narrow  band 
between  Canoas  Creek  and  the  region  of  Big  Tar  Canyon. 


108 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


GENERAL  GEOLOGY  AND  OCCURRENCE  OF  OIL. 

Reef  Ridge  and  the  region  immediately  adjacent  to  it  both  south- 
west and  northeast  lies  on  the  eastern  flank  of  the  great  monocline  of 
rocks  which  forms  the  main  Diablo  Range.  The  formations  involved 
in  the  geology  are  the  Knoxville-Chico  (Cretaceous,  conglomerates, 
sandstones,  and  shales),  the  Tejon  (Eocene,  sandstones  and  shales), 
the  Vaqueros  (lower  Miocene,  sandstone  and  shale),  the  Santa  Mar- 
garita (upper  middle  Miocene,  shale),  and  the  Jacalitos  (upper  Mio- 
cene, sandstone,  shale,  and  gravel).  The  oil,  as  in  the  region  of  the 
Coalinga  field  proper,  is  believed  to  have  originated  in  the  shales  of 
the  Tejon  formation,  but  has  migrated  to  the  underlying  sandstones 
of  the  Tejon,  into  sands  interbedded  with  the  shales  of  the  Tejon, 
and  into  the  overlying  Vaqueros  sandstone.  Evidence  of  the  petro- 
liferous character  of  the  Tejon  and  Vaqueros  is  found  in  numerous 
tar  springs  which  emanate  from  those  formations  at  various  points 
within  the  area  under  discussion.  Such,  for  instance,  are  those  in 
Canoas  Creek,  which  come  from  the  upper  part  of  the  Vaqueros; 
those  on  or  near  the  Clark  ranch  farther  south  in  the  vicinity  of  Garza 
Creek  in  the  same  formation  as  the  latter;  the  famous  tar  spring  in 
Big  Tar  Canyon,  which  comes  from  the  upper  part  of  the  Tejon;  and 
the  springs  in  Little  Tar  Canyon  and  north  of  it,  which  emanate  from 
the  upper  part  of  the  Tejon.  Numerous  other  seepages  and  springs 
are  found  along  the  outcrop  of  the  Tejon  and  Vaqueros;  but  within 
the  area  mapped  none,  to  the  knowledge  of  the  writers,  are  found 
farther  north  than  Canoas  Creek  nor  farther  south  than  the  head  of 
Little  Tar  Canyon. 

Indications  of  petroleum  are  found  in  the  basal  shale  layers  in  the 
Tent  Hills  anticline,  2 miles  southeast  of  Dudley,  but  no  true  seepages 
are  known  between  the  one  in  Little  Tar  Canyon  and  Sulphur  Spring 
in  the  Devils  Den  district.  The  Castle  Mountain  fault,  which  cuts 
off  the  Tejon  and  Vaqueros  near  the  head  of  Little  Tar  Canyon,  is 
believed  also  to  eliminate  these  same  formations  under  the  Santa 
Margarita  southward  for  a considerable  distance  below  the  head  of 
Little  Tar  Canyon.  Owing  to  the  steep  dip  in  the  formations  along 
Reef  Ridge  the  petroliferous  zone  is  necessarily  very  narrow.  The 
extent  of  the  zone  in  which  it  seems  possible  that  productive  wells 
may  be  put  down  is  shown  on  the  map  (PI.  I).  Water  accompanies 
the  oil  in  all  of  the  seepages  along  this  belt  and  has  caused  the  failure 
of  many  of  the  test  holes  that  have  been  put  down  in  the  area. 

GEOLOGY  OF  THE  WELLS. 

The  wells  in  the  Kreyenhagen  field  may  be  divided  into  two  groups ; 
those  which  have  been  sunk  in  the  Tejon  (Eocene)  formation,  and 
those  which  start  in  strata  above  or  younger  than  the  Tejon.  The 


THE  OIL  FIELDS. 


109 


wells  in  the  first  group,  enumerated  from  north  to  south,  include 
those  of  the  Kreyenhagen  Oil  Company,  Kings  County  Oil  Company, 
Consolidated  Oil  and  Development  Company,  Baby  King  Oil  Com- 
pany, and  Avenal  Land  and  Oil  Company.  The  wells  in  the  second 
group  enumerated  in  the  same  direction  include  those  of  the  Black 
Mountain  Oil  Company,  Kings  County  Oil  Company,  St.  Lawrence 
Oil  Company,  and  that  of  the  El  Cerrito  Oil  Company,  formerly  known 
as  the  Anderson  well. 

Tej on  formation. — The  two  wells  of  the  Kreyenhagen  Oil  Company 
are  located  on  Canoas  Creek  in  the  SE.  J sec.  32,  T.  22  S.,  R.  16  E. 
Both  wells  start  in  the  shale  in  the  upper  part  of  the  Tej  on,  the  south- 
ermost,  well  No.  1,  beginning  lowest  in  the  formation.  This  well 
(No.  1)  penetrated  650  feet  of  dark-colored  shale,  finding  water  at 
125  and  at  400  feet,  and  ended  in  10  feet  of  oil  sands. 

An  examination  of  the  geology  immediately  south  of  this  well  indi- 
cates that  the  oil  sand  is  very  much  thicker  than  indicated;  just  how 
far  below  the  shale  the  sand  is  impregnated  it  was  not  possible  to 
determine  accurately,  but  on  the  surface  the  sand  showed  signs  of 
petroleum  for  a thickness  of  over  100  feet.  Well  No.  1 is  said  to  have 
yielded  about  15  barrels  a day  at  the  start,  soon  falling  to  5 or  6 
barrels.  The  product  is  said  to  be  a light-green  oil,  gravity  between 
37°  and  38°  B.  No  water  accompanied  the  oil.  Well  No.  2 of  the 
same  company  is  located  north  of  and  higher  in  the  formation  than 
well  No.  1.  It  is  said  to  have  found  traces  of  oil  at  1,000  and  1,100 
feet  and  to  have  attained  a depth  of  about  1,200  feet,  at  which  point 
water  was  encountered.  This  last  well  never  produced  commercial 
quantities  of  oil. 

The  Kings  County  Oil  Company  sunk  a well  in  the  SW.  \ SW.  J 
sec.  3,  T.  23  S.,  R.  16  E.  This  location  implies  that  the  well  started 
somewhere  about  the  middle  of  the  band  of  the  Tej  on  formation  as 
developed  in  this  vicinity.  The  well  is  said  to  have  passed  through 
black  shale,  blue  sandstone,  and  brown  sandstone  containing  oil,  but 
was  abandoned  on  account  of  water. 

The  Consolidated  Oil  and  Development  Company  sunk  tw~o  wells 
in  the  Tejon  (Eocene)  formation  in  the  NE.  \ sec.  10,  T.  23  S.,  R.  16 
E.  One  of  the  wells  attained  a depth  of  1,100  feet  and  is  said  to  have 
obtained  a good  showing  of  20°  B.  amber-colored  oil  at  a depth  of 
1,050  feet.  The  difference  in  gravity  between  this  oil  and  that 
obtained  from  the  same  formation  in  the  Kreyenhagen  well  is  not 
easily  explained. 

The  well  of  the  Baby  King  Oil  Company  is  located  in  the  canyon 
of  the  first  stream  west  of  Big  Tar  Canyon*,  immediately  behind  Reef 
Ridge,  in  the  NE.  \ sec.  11,  T.  23  S.,  R.  16  E It  starts  in  strata 
lying  near  the  contact  between  the  Tejon  (Eocene)  and  Vaqueros 
(lower  Miocene)  formations.  It  is  said  to  have  struck  oil  of  30°  B. 


110 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


gravity  at  400  feet,  and  oil  of  18°  B.  gravity  at  1,100  feet;  a short 
distance  below  this  last  point  flowing  water  was  encountered.  At 
the  time  of  the  writer’s  visit,  in  September,  1907,  the  well  was  flowing 
about  half  a miner’s  inch  of  water,  accompanied  by  occasional  blebs 
of  black  heavy  oil  and  some  gas. 

The  Avenal  Land  and  Oil  Company  has  two  wells  in  the  E.  J E.  | 
sec.  18,  T.  23  S.,  R.  17  E.,  not  far  from  the  famous  tar  spring  in  Big 
Tar  Canyon.  Well  No.  1,  the  westernmost  of  the  two,  starts  down 
in  the  soft  oil-stained  sand  beds  of  the  Tejon  (Eocene),  or  possibly 
Vaqueros  (lower  Miocene),  immediately  underlying  the  lowest 
hard  sandstone  bed  of  the  Vaqueros.  The  log  of  this  well  is  as 
follows: 


Log  of  well  No.  1 , Avenal  Land  and  Oil  Company,  E.  \ E.%  sec.  18,  T.  23,  S.,  R.  17  E. 


Adobe 

Oil  sand  with  water 

Blue  water  sand 

Clay 

Shale 

Oil  sand 

Shale 

Sand  showing  traces  of  oil 

Shale 

Blue  clay 

Sand  with  traces  of  oil  (not  finished) 


Feet. 

20 

70 

140 

235 

521 

555 

590 

635 

802 

900 

984 


This  well  is  said  to  have  yielded  less  than  2 barrels  a day  of  dark- 
colored  28°  B.  oil.  Well  No.  2 starts  well  down  in  the  Tejon  and  is 
said  to  have  gone  through  soft  sand  to  1,045  feet,  where  a productive 
sand  was  encountered.  It  yielded  some  oil  when  pumped  by  a 
bailer. 

Formations  above  the  Tejon. — The  Black  Mountain  Oil  Company 
sunk  two  wells  in  the  SW.  J NW.  I sec.  33,  T.  22  S.,  R.  16  E.  Both 
start  in  the  dark  shale  of  the  Santa  Margarita  formation  and  obtain 
their  oil  from  the  top  of  the  Vaqueros  sandstone.  The  log  of  well 
No.  1 of  this  company  is  as  follows: 


Log  of  well  No.  1,  Black  Mountain  Oil  Company,  &TF.  | NW.  \ sec.  33,  T.  22  S.,  R.  16  E. 


Feet. 

Dark-colored  shale 80 

White  sand 85 

Dark-colored  shale 400 

Light-colored  shale 550 

Shale  and  sand  with  oil 570 

Light-colored  shale r 640 

Oil  sand 660 

Shale 700 

Oil  sand 720 


THE  OIL  FIELDS. 


Ill 


This  well  is  said  to  have  produced  5 or  6 barrels  of  black,  18°  B. 
oil.  The  second  well  is  located  600  feet  north  of  No.  1,  but  no  data 
concerning  it  are  available. 

The  Kings  County  Oil  Company  sunk  a well  in  the  SW.  \ NE.  J 
sec.  3,  T.  23  S.,  R.  16  E.,  which  is  believed  to  start  toward  the  bottom 
of  the  Santa  Margarita  (upper  middle  Miocene)  and  to  obtain  its 
oil  from  the  Vaqueros  (lower  Miocene).  The  log  of  this  well  is  as 
follows : 


Log  of  well  of  Kings  County  Oil  Company  in  &TF.  j-  NE.  \ sec.  3,  T.  23  S.,  R.  16  E. 


Clay  and  soil 

White  shale 

Black  shale 

Black  sand 

Black  shale 

Hard  gravel  (heavy  oil  at  240  feet).. 

Black  shale 

Gravel 

Black  shale 

Blue  sand  rock 

Water  sand 

Blue  sand  rock 

Sand 

Clayey  sandstone 

Black  shale 

Clayey  sandstones 

Hard  shale 

Hard  rock,  sandstone  predominating 


Feet. 

12 

29 

65 

67 

90 

120 

275 

285 

410 

450 

490 

540 

556 

600 

660 

696' 

720 

950 


Another  well  was  also  started  by  the  same  company  but  was  never 
finished. 

The  St.  Lawrence  Oil  Company  is  said  to  have  sunk  a well  in  the 
SE.  \ NE.  J sec.  12,  T.  23  S.,  R.  16  E.,  which  encountered  oil  near 
the  bottom.  This  well  doubtless  began  in  the  shale  of  the  Santa 
Margarita  and  penetrated  the  oil  sands  at  the  top  of  the  Vaqueros 
(lower  Miocene). 

A.  M.  Anderson  and  associates  (El  Cerrito  Oil  Company)  have  been 
drilling  the  past  summer  on  a well  in  the  NW.  J sec.  14,  T.  23  S., 
R.  17  E.  The  well  starts  near  the  contact  between  the  Etchegoin 
(upper  Miocene)  and  Paso  Robles  (Pliocene-Pleistocene)  formations, 
and  is  said  to  have  been  located  on  the  evidence  of  a supposed  oil 
sand  outcrop  a few  hundred  feet  south  of  the  well  site. 


KETTLEMAN  HILLS  FIELD. 


LOCATION. 

Development  work  within  the  Kettleman  Hills  has  been  confined 
to  their  northern  portion,  all  the  wells  started  having  been  put 


112 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


down  on  the  flanks  of  the  hills  at  some  distance  from  the  axis  of  the 
Coalinga  anticline,  which  runs  parallel  with  and  east  of  the  topo- 
graphic axis  of  the  hills. 

GEOLOGY  AND  INDICATIONS  OP  OIL. 

The  formations  that  rise  to  the  surface  in  the  anticline  are  the 
Etchegoin  arid  the  Paso  Robles,  described  fully  on  pages  46-61.  The 
structure  of  the  hills  is  that  of  a simple  arched  anticline,  with  low 
dips  toward  the  axis  and  steeper  ones  toward  the  flanks.  The 
maximum  dip  on  the  northeastern  flank  is  about  31°,  that  on  the 
southwestern  flank  45°. 

One  of  the  Government  land  surveyors  who  visited  the  Kettleman 
Hills  over  twenty  years  ago  informed  the  late  Mr.  W.  P.  Kerr  fwho 
informed  the  senior  author)  that  he  had  seen  what  he  supposed  was 
an  oil  seepage  in  the  northeastern  flank  of  the  hills  in  the  south- 
eastern part  of  T.  21  S.,  R.  17  E.,  or  the  northeastern  part  of  T.  22  S., 
R.  17  E.  Neither  Mr.  Kerr  nor  the  senior  author,  who  visited  this 
locality  in  1907  and  made  a careful  examination,  were  able  to  find 
any  traces  of  an  oil  seepage  in  this  region,  although  places  where 
mineral  waters  have  oozed  from  the  rocks  in  the  rainy  season  were 
noted  in  several  instances.  It  is  believed  that  the  Kettleman  Hills 
offer  no  direct  surface  evidence  of  petroliferous  deposits. 

GEOLOGY  OF  THE  WELLS. 

Seven  or  more  wells  have  been  put  down  in  the  hills  and  none  of 
these  have  been  successful,  but  owing  to  their  position  and  compara- 
tively slight  depth  they  have  made  no  adequate  test  of  the  territory. 
(See  p.  120  for  conclusions  concerning  future  development.)  Two 
wells,  the  Gibbs  and  Oceanic,  are  on  the  northeastern  flank  of  the 
anticline;  the  other  five  are  on  the  southwestern  flank.  None  are 
within  the  area  outlined  as  possibly  productive  on  the  map  (PI.  I). 

Following  are  descriptions  of  the  wells  that  have  been  put  down 
in  the  Kettleman  Hills: 

Gibbs  Oil  Company,  located  in  eastern  part  of  the  NW.  \ sec.  28,  T.  21  S.,  R.  17  E., 
farthest  north  of  any  in  the  Kettleman  Hills.  Starts  in  beds  near  the  top  of  the 
Etchegoin  (upper  Miocene)  formation  about  1 mile  east  of  the  axis  of  the  Coalinga 
anticline. 

Oceanic  Oil  Company’s  well;  located  in  the  NW.  \ sec.  1,  T.  22  S.,  R.  17  E.,  on 
northeastern  flank  of  Coalinga  anticline  on  one  of  the  spur  ridges  running  northeast 
from  the  main  Kettleman  Hills  divide.  Starts  in  the  uppermost  blue-gray  sands  of 
the  Etchegoin;  said  to  have  penetrated  blue  sands  and  shales  and  to  have  yielded 
large  quantities  of  water;  depth,  950  feet. 

Stanislaus  Oil  Company’s  well;  located  in  the  NW.  I sec.  4,  T.  22  S.,  R.  17  E.  Starts 
in  beds  well  up  in  Etchegoin  formation,  a little  less  than  a mile  southwest  of  the 
Coalinga  anticline;  is  said  to  have  attained  a depth  of  about  1,000  feet  without  en- 
countering any  oil. 


THE  OIL  FIELDS. 


113 


Iowa  Oil  Company’s  well;  located  in  the  SW.  \ sec.  4,  T.  22  S.,  R.  17  E.,  not  far 
distant  from  and  on  the  same  ridge  as  that  of  the  Stanislaus  Oil  Company.  Conditions 
in  the  two  wells  are  practically  the  same  and  results  obtained  were  similar. 

Florence  Oil  Company’s  wells;  both  located  in  the  NW.  4 sec.  15,  T.  22  S.,  R.  17  E. 
On  the  southwestern  flank  of  the  Coalinga  anticline  about  a mile  from  the  axis;  near 
the  surface  penetrate  strata  at  the  bottom  of  the  Paso  Robles  formation.  Are  said  to 
have  attained  a depth  of  720  feet  and  to  have  encountered  considerable  gas  but  no  oil. 

Esperanza  Oil  Company’s  wells;  both  located  in  the  SW.  \ sec.  14,  T.  22  S.,  R.  17  E. 
One  attained  a depth  of  1,100  feet  but  was  abandoned  on  account  of  water;  the  other 
reached  840  feet  when  drilling  operations  were  suspended.  Start  in  the  uppermost 
beds  of  the  Etchegoin  formation,  on  southwestern  flank  of  the  anticline  something 
over  a mile  from  the  axis. 

Stockton  Oil  Company’s  well;  located  in  the  NW.  \ sec.  30,  T.  22  S.,  R.  18.  E., 
farthest  south  of  any  test  well  in  the  hills.  Starts  in  beds  near  the  contact  between 
the  Etchegoin  and  Paso  Robles  formations,  on  southwestern  flank  of  the  anticline 
about  2 miles  distant  from  the  axis.  Is  said  to  have  attained  a depth  of  670  feet,  with 
no  results  in  the  way  of  gas  or  oil. 

FUTURE  DEVELOPMENT. 

GENERAL  STATEMENT. 

The  conclusions  here  to  be  discussed  as  to  the  course  that  future 
development  will  take  in  the  Coalinga  district  are  based  on  the  belief 
that  the  petroleum  is  originally  derived  from  the  shales  of  the  Tejon 
(Eocene)  formation  and  that  on  migration  it  collects  both  in  the 
sands  interbedded  with  these  shales  and  in  the  porous  portions  of 
the  overlying  Miocene.  All  of  the  conditions  indicate  that  this 
belief  is  well  founded  and  is  equivalent  to  the  truth. 

Several  requisite  factors  enter  into  the  question  of  the  accumula- 
tion of  the  petroleum  and  the  possibility  of  its  extraction  in  com- 
mercial quantities.  Among  these  are  the  following,  briefly  stated: 

(a)  An  adequate  thickness  of  the  shales  of  the  Tejon  (Eocene)  to 
yield  commercial  quantities  of  oil. 

(b)  A cause  for  the  migration  of  the  oil  from  its  source  in  the 
organic  shales.  This  cause  is  believed  to  be  supplied  by  the  tend- 
ency of  oil  to  migrate  by  diffusion  through  certain  media,  such  as 
dry  shales;  it  may  be  and  doubtless  is  in  certain  instances  aug- 
mented by  hydrostatic  pressure  vdierever  water  has  come  in  contact 
wdth  the  petroleum. 

(c)  Associated  porous  beds  occupying  such  a position  relative  to 
the  source  of  the  oil  and  to  impervious  barriers  as  to  permit  of  the 
petroleum  passing  from  the  source  into  the  final  reservoir  and  being 
there  confined  by  impervious  strata.  Wet  shale  or  clay  and  certain 
fine-grained  wrater-impregnated  sands  are  believed  to  be  among  the 
effective  barriers  to  the  migration  of  the  oil. 

(d)  Occurrence  of  the  accumulations  at  a depth  far  enough  below 
the  surface  and  distant  enough  from  outcrops  to  preclude  the  escape 

52332— Bull.  357—08 8 


114 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


of  the  lighter  hydrocarbons,  and  still  at  depths  which  may  be  profit- 
ably reached  by  the  drill.  The  areas  within  the  lines  shown  on  the 
map  (PI.  II)  as  bounding  the  possibly  productive  territory  are  those 
in  which  the  top  of  the  supposed  oil  zone  has  been  calculated  as  pos- 
sibly within  a vertical  distance  of  4,500  feet  from  the  surface.  A 
depth  of  4,500  feet  below  the  surface  has  been  arbitrarily  taken  as 
the  maximum  to  which  it  is  possible  to  drill  by  present  methods  in 
the  region  under  discussion,  as  this  is  about  the  maximum  depth  of 
holes  in  California  which  have  been  drilled  with  a standard  rig.  It 
may  be  possible  to  go  deeper  than  this,  but  for  the  present  this  limit 
seems  sufficiently  great.  Whether  or  not  a well  can  be  profitably 
drilled  depends  upon  so  many  factors,  such  as  quantity  of  oil  pro- 
duced compared  with  cost  of  drilling,  price  of  oil,  etc.,  that  local 
conditions  must  determine  the  result  in  each  specific  case. 

It  seems  very  unlikely  that  oil,  even  in  small  amounts,  will  be  found 
in  any  of  the  rocks  underlying  the  Tejon  (Eocene) — that  is,  in  the 
Cretaceous  or  Franciscan  formations  (see  map,  PI.  I) — while  it  is 
quite  likely  that  it  will  be  found  in  the  Tejon  and  in  the  formations 
immediately  overlying  the  latter,  whether  or  not  in  paying  quanti- 
ties depending  on  the  factors  above  enumerated.  In  the  following 
paragraphs  it  is  the  intention  of  the  writers  to  give  their  personal 
opinion  as  to  the  probabilities  of  the  occurrence  of  petroleum  in 
regions  not  yet  thoroughly  tested  by  the  drill.  It  must  be  borne  in 
mind,  however,  that  absolute  determination,  by  work  on  the  sur- 
face, of  the  occurrence  or  nonoccurrence  of  oil  in  any  one  locality 
is  not  possible.  The  best  that  can  be  done  is  to  calculate  the  degree 
of  probability  on  the  basis  of  surface  indications  and  structural  con- 
ditions. 

AREAS  DISCUSSED. 

The  areas  for  which  the  probabilities  of  the  occurrence  of  petro- 
leum is  discussed  in  the  following  paragraphs  are  as  follows:  North- 
west of  Eastside  field,  Eastside  field,  Anticline  Ridge  and  Guijarral 
Hills,  Westside  field,  south  of  Waltham  Creek  on  Jacalitos  anticline, 
Reef  Ridge  south  to  Dagany  Gap,  and  Kettleman  Hills. 

NORTHWEST  OF  EASTSIDE  FIELD. 

The  well  of  T.  C.  Oil  Company  in  sec.  2,  T.  19  S.,  R.  15  E.,  has 
proved  the  eastern  flank  of  the  Coalinga  anticline  as  far  north  as  the 
northern  edge  of  the  area  shown  on  the  map  (PL  I).  Near  this  point 
the  beds  bend  from  a strike  of  almost  due  north  to  one  of  N.  30°  or 
40°  W.,  the  dip  at  the  same  time  steepening  to  30°  or  more  in  secs.  34 
and  35,  T.  18  S.,  R.  15  E.  The  writers  have  examined  the  country 
only  as  far  north  as  the  middle  of  sec.  29,  T.  18  S.,  R.  15  E.,  but  up 
to  this  point  the  shales  of  the  Tejon  (Eocene)  were  found  well  devel- 
oped, and  it  is  therefore  believed  that  the  overlying  Miocene  sands 


THE  OIL  FIELDS. 


115 


will  be  found  productive  as  in  the  region  farther  south.  The  steep- 
ening of  the  dip  of  the  beds  in  this  undeveloped  territory  will  neces- 
sarily narrow  the  productive  ground  materially,  decreasing  it  to  a 
band  less  than  2 miles  wide,  whereas  southward  in  the  middle  of  the 
Eastside  field,  where  the  dip  is  approximately  only  16°,  the  width 
of  the  productive  belt  is  over  3 miles.  Toward  the  northern  end  of 
the  Eastside  field  as  mapped  in  this  report,  and  still  farther  north- 
west, only  zone  D,  the  lower  part  of  the  Vaqueros  (lower  Miocene), 
it  is  believed,  will  be  found  productive,  and  here  not  as  prolifically 
as  farther  south,  owing  to  the  thinning  of  the  productive  zone. 

EASTSIDE  FIELD. 

Little  need  be  said  concerning  the  probable  development  in  the 
already  well-proved  areas  of  the  Eastside  field,  as  their  future  may 
be  inferred  from  a perusal  of  the  paragraphs  devoted  to  the  discus- 
sion of  the  geology  of  their  wells.  It  should  be  borne  in  mind,  how- 
ever, that  the  lower  part  (and  what  in  sec.  28  and  the  western  part 
of  secs.  22  and  27  is  the  richest  part)  of  the  oil  measures  has  not  been 
tested  in  those  wells  farthest  down  the  dip  and  should  yield  good 
returns  for  the  extra  cost  of  deepening  if  water  is  not  encountered 
at  the  greater  depth;  and  there  is  no  evidence  at  present  indicating 
that  water  exists  at  the  base  of  the  oil  in  this  area.  It  is  believed 
that  oil  in  commercial  quantities  will  never  be  found  above  the 
“Big  Blue”  in  the  Eastside  field  (a  possible  exception  to  this  may 
be  the  “St.  Paul  sand”  in  sec.  34),  so  that  wells  put  down  outside 
of  the  limit  of  those  in  which  the  bottom  of  the  “Big  Blue”  is  pene- 
trated at  less  than  4,500  feet  will  probably  never  pay. 

Two  factors  militate  against  the  successful  exploitation  of  the 
southwestern  flank  of  the  Coalinga  anticline  immediately  southwest 
of  the  developed  Eastside  territory.  These  are  (a)  the  steep  dip 
(almost  perpendicular  in  places)  of  the  beds,  which  carries  the  oil 
zone  rapidly  downward  to  great  depths  toward  the  southwest,  and 
(b)  the  more  locally  disturbed  condition  of  the  various  beds  through- 
out this  zone  of  steep  dip.  It  is  believed  that  at  least  the  lower  part 
of  the  oil  zone  along  this  flank  will  be  found  more  or  less  productive 
wherever  it  can  be  reached,  but  it  is  also  believed,  and  this  belief  is 
strengthened  by  the  experience  of  those  who  have  drilled  in  the 
territory,  that  the  disturbed  conditions  of  the  beds  will  make  the 
shutting  off  of  the  water  difficult  or  sometimes  impossible,  thus  hin- 
dering the  most  successful  manipulation  of  the  wells.  Toward  the 
southeastward  the  dips  lessen  in  degree  and  the  resulting  conditions 
are  somewhat  more  favorable  for  successful  wells. 

Within  the  area  of  the  shale  and  interbedded  sandstone  of  the 
Tejon  (Eocene)  lying  between  the  Cretaceous  (Chico)  beds  on  the  west 
and  the  overlying  Vaqueros  (lower  Miocene)  sandstone  on  the  east 


116 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


and  extending  from  Oil  City  northward  beyond  secs.  29  and  30, 
T.  18  S.,  R.  15  E.,  it  is  believed  that  favorable  locations  for  produc- 
tive wells  yet  remain  undeveloped.  Surface  indications  lead  to  the 
belief  that  wherever  in  this  area  the  sands  interbedded  with  the  shale 
of  the  Tejon  formation  are  of  a porous  character  they  contain  appre- 
ciable and  in  some  cases  probably  commercial  quantities  of  petroleum 
at  available  depths.  As  the  quality  of  the  oil  obtained  from  the  Tejon 
sands  is  usually  considerably  higher  than  that  found  in  the  Miocene, 
small  producers  in  the  Tejon  area  should  pay  where  the  same  produc- 
tion would  involve  a loss  elsewhere.  It  is  believed  that  a well  site  so 
chosen  that  the  prospective  sand  would  be  encountered  at  600  feet  or 
more  below  the  surface  would  be  the  most  favorable  for  exploiting  the 
Tejon  territory.  The  same  conclusions  as  those  just  expressed  have 
been  reached  for  practically  the  whole  band  of  Tejon  extending  inter- 
mittently along  the  western  edge  of  the  Miocene  in  the  Coalinga  dis- 
trict from  sec.  29,  T.  18  S.,  It.  15  E.,  to  Little  Tar  Canyon,  northeast 
of  Dudley.  Furthermore,  it  is  believed  that  productive  sands  in  the 
Tejon  may  be  tapped  by  wells  which  start  in  overlying  formations, 
but  predictions  as  to  favorable  locations  for  such  tests  would  be 
unreliable  owing  to  the  unconformable  relation  of  the  overlying  beds 
to  the  Tejon. 

ANTICLINE  RIDGE  AND  GUIJARRAL  HILLS. 

Throughout  its  entire  length  along  the  southwestern  edge  of  the 
developed  territory  in  the  Eastside  field  the  axis  of  the  Coalinga  anti- 
cline dips  southeast  at  about  9°  until  in  the  northwestern  part  of 
sec.  2,  T.  20  S.,  R.  15  E.,  it  assumes  an  angle  of  approximately  4°. 
The  territory  along  this  comparatively  low-dipping  portion  of  the 
anticline  has  been  proved  productive  as  far  southeastward  as  the 
middle  of  the  NW.  \ sec.  2,  T.  20  S.,  R.  15  E.  Southeastward  from 
this  last-mentioned  locality  the  indications  for  productive  wells  are 
good.  The  productive  territory  will  be  limited  to  that  portion  of 
the  anticline  where  the  productive  sands  lie  at  such  a depth  as  to  be 
profitably  reached  by  the  drill. 

In  drawing  conclusions  as  to  just  how  far  southeastward  along  the 
axis  of  the  anticline  this  limit  will  be  two  factors  have  to  be  taken 
into  consideration:  (a)  Dip  or  pitch  of  the  anticline,  and  ( b ) thicken- 
ing of  the  formations  toward  the  southeast. 

Regarding  the  first  factor  (a)  surface  evidence  indicates  a dip  of 
about  4°,  or  something  like  350  feet  to  the  mile.  Certain  evidence 
offered  by  the  well  logs  of  the  territory  in  question,  however,  indicate 
a much  lower  dip,  about  2°,  or  185  feet  to  the  mile. 

Regarding  the  second  factor  ( b ) a conservative  estimate  indicates 
that  at  its  nearest  point  to  the  surface  in  the  northern  portion  of  the 
Kettleman  Hills  the  top  of  the  oil-bearing  zone  may  lie  within  3,500 


THE  OIL  FIELDS. 


117 


feet  of  the  surface.  This  depth  assumes  a very  considerable  increase 
in  the  thickness  of  the  formations  above  the  oil-bearing  Yaqueros  over 
the  thickness  of  the  same  formations  in  the  Eastside  field.  Just 
where  this  thickening  of  the  beds  begins  it  is  not  possible  to  find  out, 
but  it  is  believed  to  commence  toward  the  lower  end  of  Anticline 
Ridge;  that  is,  along  the  Coalinga  anticline  a little  way  north  of  the 
railroad.  Taking  all  of  the  evidence  into  consideration,  it  seems 
probable  that  the  conditions  indicated  by  the  contours  on  the  map 
(PI.  II),  a dip  of  4°,  or  350  feet  to  the  mile,  along  the  anticline,  will 
be  found  to  be  the  average  as  far  southeastward  as  the  Guij  arral  Hills, 
although  it  may  possibly  be  less  in  secs.  2 and  12,  T.  20  S.,  R.  15  E., 
and  possibly  somewhat  more  in  the  region  of  the  Guij  arral  Hills. 
Owing  to  the  much  steeper  dip  on  the  southwestern  flank  of  the  anti- 
cline than  on  the  northeastern,  the  productive  ground  will  be  found 
to  extend  much  farther  away  from  the  axis  on  the  latter  flank  than  on 
the  former,  as  indicated  by  the  contour  map. 

WESTSIDE  FIELD. 

Owing  to  the  rapid  thinning  and  even  entire  pinching  out  of  the 
Yaqueros  or  lower  Miocene  oil-bearing  formation  toward  the  western 
edge  of  the  Westside  field,  predictions  as  to  the  exact  depths  at  which 
the  top  of  this  formation  will  be  encountered  at  any  particular  point 
are  unusually  hazardous.  For  this  reason  the  top  of  the  lowest  of  the 
Jacalitos  (upper  Miocene)  petroliferous  zones  (zone  B)  was  chosen 
for  contouring,  as  this  latter  extends  over  the  whole  region,  although 
both  at  the  northern  and  the  southern  ends  of  the  field  it  is  not  com- 
mercially productive.  There  are  no  known  reasons  at  present  for 
believing  that  any  of  the  territory  in  the  main  portion  of  the  Westside 
field  under  which  the  productive  measures  lie  at  a greater  depth  than 
500  feet  are  unproductive.  Local  conditions,  such  as  the  extreme 
thinness  of  the  shale  or  clay  separating  water  from  oil  sands,  may 
make  the  manipulation  of  certain  wells  more  or  less  difficult  or  pos- 
sibly unsuccessful,  but  there  is  no  evidence  of  “bottom”  or  “edge” 
water  in  any  of  the  wells  so  far  drilled  that  condemns  any  of  the  ter- 
ritory generally  considered  as  proved.  On  the  contrary,  evidence  is 
available  indicating  that  in  many  of  the  wells  which  have  penetrated 
but  a short  distance  into  the  oil-bearing  zone  there  are  underlying  and 
untouched  sands  even  more  productive  than  those  already  developed. 
It  is  the  belief  of  the  writers  that  in  this  field,  as  in  the  Eastside,  the 
sands  become  more  productive  the  nearer  they  lie  to  the  brown  shale 
of  the  Tejon.  It  seems  worth  while,  therefore,  in  those  areas  where 
conditions  are  such  that  water  could  be  plugged  off  if  encountered 
below  the  already  tested  productive  sands,  to  deepen  to  the  beds  imme- 
diately overlying  the  brown  shale.  Such  a procedure,  however,  will 
require  great  care  in  avoiding  the  flooding  of  the  upper  productive 


118  COALINGA  OIL  DISTRICT,  CALIFORNIA. 

beds  if  water  should  happen  to  be  encountered  in  the  oil-bearing 
series  of  beds. 

It  is  believed  that  considerable  commercially  productive  territory 
is  yet  untested  in  the  southwestern  portion  of  the  Westside  field, 
especially  north  and  northeast  of  the  fault  (see  Pl.  II)  which  extends 
east  and  west  through  the  middle  of  the  SW.  J sec.  12,  T.  21  S., 
R.  14  E.  The  extent  of  this  productive  area  is  believed  to  depend 
on  whether  the  various  Miocene  sands  are  underlain  by  theTejon 
(Eocene)  formation  or  by  Knoxville-Chico  (Cretaceous)  rocks.  In 
the  former  case  it  is  believed  that  the  beds  will  be  found  commercially 
productive;  in  the  latter  case,  except  within  half  a mile  or  so  of  the 
contact  between  the  Tejon  and  the  Knoxville-Chico,  it  is  believed 
the  oil  sands  will  be  dry  or  only  poorly  saturated.  Direct  evidence 
of  the  trend  of  the  contact  between  the  Knoxville-Chico  and  Tejon 
ceases  in  the  southwest  corner  of  sec.  26,  T.  20  S.,  R.  14  E.,  because 
south  of  there  it  is  entirely  covered  by  the  later  formations.  At  this 
locality  its  direction  is  about  S.  25°  E.,  but  this  strike  is  believed  to 
swing  eastward  so  that  the  contact  passes  north  of  the  corner  of 
secs.  1,  12,  6,  and  7.  The  partial  failure  of  the  well  in  the  SE.  \ sec.  12 
is  believed  to  be  due  entirely  to  local  conditions  accompanying  the 
fault  to  the  north  of  the  well,  while  the  water  in  the  well  in  the  SE.  I 
sec.  12  comes  from  beds  believed  to  be  Knoxville-Chico. 

JACALITOS  ANTICLINE. 

The  first  locality  south  of  the  southwest  corner  of  sec.  26,  T.  20  S., 
R.  14  E.,  where  the  Tejon  (Eocene)  formation  is  definitely  known,  is  in 
Sulphur  Spring  Canyon  in  the  southern  part  of  sec.  23,  T.  22  S., 
R.  15  E.  As  mentioned  above,  there  is  evidence  that  the  con- 
tact between  the  Knoxville-Chico  and  the  Tejon  passes  north  of 
the  corner  of  secs.  1 and  12,  T.  21  S.,  R.  14  E.,  and  secs.  6 and  7, 
T.  21  S.,  R.  15  E.  Just  how  this  contact  trends  between  this 
corner  and  the  Sulphur  Spring  Canyon  locality  is  not  definitely 
known,  but  it  is  the  belief  of  the  writers  after  a study  of  the  inter- 
vening region  that  the  contact  soon  bends  to  the  south  after  passing 
into  the  northern  part  of  sec.  7,  T.  21  S.,  R.  15  E.,  then  swings  around 
to  a southwesterly  trend,  continuing  this  down  to  Sulphur  Spring 
Canyon,  in  a somewhat  similar  way  to  that  followed  by  the  later  beds, 
now  exposed  over  the  area.  The  relation  of  the  whereabouts  of  this 
contact  between  the  Knoxville-Chico  and  Tejon  to  the  future  develop- 
ment of  the  region  is  obvious  when  it  is  remembered  that  only  those 
portions  of  the  Miocene  sands  which  overlie  the  Tejon  (Eocene)  are 
believed  to  be  productive.  It  is  the  opinion  of  the  writers,  therefore, 
that  the  basal  Miocene  sands  are  likely  to  be  commercially  oil  bearing 
only  in  the  area  northeast  of  a line  which  passes  in  a general  way 
southwesterly  from  the  eastern  part  of  sec.  7,  T.  21  S.,  R.  15  E.,  to 


THE  OIL  FIELDS. 


119 


sec.  23,  T.  22  S.,  R.  15  E.  Passing  southward  from  the  region  imme- 
diately north  of  Alcalde  Canyon  the  formations  which  overlie  the  oil- 
bearing Vaqueros  thicken  rapidly  until  in  the  region  *of  Jacalitos 
Creek,  the  Jacalitos  formation  (upper  Miocene)  alone  is  3,500  feet 
through,  whereas  in  the  Alcalde  Canyon  region  it  is  less  than  1,500 
feet.  This  great  thickening  of  the  beds  above  the  oil  zone  toward  the 
south  will  necessitate  much  deeper  wells  than  would  be  required  if  the 
formations  were ' uniform.  At  the  axis  of  the  Jacalitos  anticline  on 
Jacalitos  Creek,  where  the  supposedly  productive  zone  approaches 
nearest  to  the  surface,  it  is  estimated  that  the  top  of  the  Vaqueros  is 
about  3,600  feet  below  the  surface.  As  the  axis  plunges  northward 
north  of  the  creek  and  southward  along  the  anticline  from  the  high 
hill  immediately  south  of  the  creek  it  is  obvious  that  the  territory  pos- 
sible of  development  is  very  limited.  The  northeastern  flank  of  the 
Jacalitos  anticline  dips  much  more  steeply  than  the  southwestern 
flank,  so  that  the  band  of  productive  ground  on  the  northeast  will  be 
much  narrower  than  that  on  the  southwest.  Owing  to  the  uncertain- 
ties incident  to  the  complicated  structure  at  the  northern  end  of  the 
Jacalitos  anticline  in  sec.  18,  T.  21  S.,  R.  15  E.,  and  the  rapid  rate 
of  thickening  of  the  beds,  quantitative  statements  concerning  the 
depth  of  the  oil  zone  below  the  surface  at  any  one  point  will  not  be 
attempted  for  the  region  south  of  Alcalde  Canyon.  A suggestion  as  to 
the  probable  depth  at  which  the  oil  zone  lies  may  be  gathered  from 
the  statement  that  it  is  struck  at  about  700  feet  below  sea  level  (1,600 
feet  below  the  surface  in  the  NW.  \ sec.  18,  T.  2lS.,R.  15E.)  and  as 
before  stated  is  probably  some  2,800  feet  below  sea  level  (3,600  below 
the  surface)  on  the  axis  of  the  anticline  on  Jacalitos  Creek.  This 
great  increase  in  depth  occurs  even  in  the  face  of  the  fact  that  the  axis 
of  the  anticline  is  plunging  (near  its  northwestern  end  as  much  as  15°) 
toward  the  northwest. 

REEF  RIDGE  SOUTH  TO  DAGANY  GAP. 

The  great  monocline  of  Tertiary  beds  which  flanks  Reef  Ridge  on 
the  east  and  forms  the  Kreyenhagen  Hills  is  underlain  by  the  Tejon 
formation  from  a point  at  least  as  far  north  as  Sulphur  Spring  Canyon 
(in  sec.  23,  T.  22  S.,  R.  15  E.)  to  the  head  of  Little  Tar  Canyon  (in 
sec.  35,  T.  23  S.,  R.  17  E.).  Throughout  nearly  the  whole  extent  of 
this  Tejon  band  it  shows  unmistakable  signs  of  its  petroleum  contents. 
Many  oil  seepages  also  occur  from  the  Vaqueros  sands  overlying  the 
Eocene,  so  that  there  is  no  doubt  as  to  the  presence  of  petroleum 
throughout  practically  the  whole  length  of  the  region  under  discus- 
sion. Furthermore,  productive  wells  on  Canoas  Creek,  in  Big  Tar 
Canyon,  and  elsewhere  (see  pp.  108-111)  have  proved  the  presence  of 
oil  in  commercial  quantities  in  at  least  certain  localities.  Although 
the  territory  offers  no  promise  of  a large  individual  production,  it 


120 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


is  the  belief  of  the  writers  that  productive  wells  may  be  put  down 
along  practically  the  whole  strip  of  territory  from  between  Jacalitos 
and  Canoas  creeks  to  Little  Tar  Canyon.^  West  of  Jacalitos  Creek  the 
Tejon  is  apparently  lacking  or  else  is  thin  and  insignificant;  southeast 
of  the  head  of  Little  Tar  Canyon  the  Tejon  is  cut  off  by  the  Castle 
Mountain  fault.  It  is  therefore  not  likely  that  the  productive  sands 
extend  far  either  northwest  of  Sulphur  Spring  Canyon  or  southeast  of 
the  head  of  Little  Tar  Canyon.  Indications  of  petroleum  are  in  evi- 
dence in  the  axis  of  the  Pyramid  Hills  anticline,  southeast  of  Dudley, 
and  still  farther  southeastward  toward  the  Devil’s  Den  country,  so 
that  the  extension  of  the  productive  belt  in  a southeasterly  direction 
from  Little  Tar  Canyon  is  probably  only  locally  affected  by  the  fault. 
The  lighter  oil  is  to  be  expected  in  the  Tejon  as  in  the  Coalinga  field, 
but  the  best  production  will  doubtless  be  found  in  the  Vaqueros  or 
lower  Miocene  sand.  The  production  in  either  case  will  probably  not 
be  large,  for  the  steep  dip  of  the  beds  precludes  the  conditions  neces- 
sary for  great  accumulations  of  oil.  The  steep  dip,  however,  so 
increases  the  distance  through  which  the  wells  may  penetrate  the  sand 
that  the  lack  of  complete  saturation  may  be  partly  compensated  for 
by  increased  surface  of  sand  exposed  in  the  well.  An  item  that  should 
not  be  overlooked  in  drawing  conclusions  concerning  this  strip  of  terri- 
tory is  the  probable  occurrence  of  water  in  or  closely  associated  with 
the  oil  sands.  Nearly  all  of  the  oil  seepages  in  the  region  are  accom- 
panied by  water,  and  many  of  the  test  wells  have  been  abandoned  on 
account  of  it,  so  that  trouble  from  this  source  should  not  cause  surprise 
to  those  who  may  undertake  to  exploit  the  region.  The  depth  to 
which  the  oil  sands  along  Reef  Ridge  may  be  exploited  is  limited  by 
the  relation  between  the  cost  of  drilling  plus  operation  and  the  pro- 
duction and  value  of  the  oil ; and  by  whether  or  not  the  water  that  is 
apparently  associated  with  the  oil-bearing  beds  is  1 1 bottom  ” or  “ edge ’ ’ 
water.  These  factors  are  determinable  only  by  actual  test.  The  area 
outlined  on  the  map  (PI.  I)  as  probably  productive  embraces  all  of 
the  territory  along  Reef  Ridge  in  which  it  is  thought  that  the  top  of 
the  Vaqueros  or  lower  Miocene  sands  will  be  encountered  at  a depth 
less  than  4,500  feet  below  the  surface.  At  some  localities  seepages 
indicate  that  the  productive  zone  is  near  the  base  of  the  formation ; at 
other  localities  the  evidence  favors  the  theory  that  the  top  will  be 
found  the  most  productive.  All  of  the  evidence  seen  by  the  writers 
leads  to  the  conclusion  that  productive  bodies  of  petroleum  will  not  be 
encountered  in  or  above  shale  of  the  Santa  Margarita  formation,  that 
is,  above  the  top  of  the  Vaqueros  (lower  Miocene)  zone. 

KETTLEMAN  HILLS. 

The  Kettleman  Hills  were  formed  by  an  uplift  of  the  sedimentary 
formations  of  this  region  along  the  Coalinga  anticline.  It  is  an  inter- 
esting and  important  problem  to  consider  whether  this  great  arch,  the 


THE  OIL  FIELDS. 


121 


summit  of  which  has  subsequently  been  in  large  part  worn  away  by 
erosion,  has  brought  within  reach  of  the  surface  the  beds  which  are 
oil-bearing  a few  miles  away.  The  conditions  for  the  accumulation 
and  preservation  of  oil  in  this  broad,  regular  fold,  would  appear  to  be 
good,  and  the  question  as  to  the  occurrence  of  valuable  deposits 
resolves  itself  principally  into  two  problems;  (1)  whether  the  hills  are 
underlain  by  the  Tejon,  the  original  oil-bearing  formation  in  this  dis- 
trict, and  whether  oil  is  therefore  most  probably  present;  and  (2) 
whether  the  oil-bearing  beds  are  brought  sufficiently  near  to  the  surface 
by  the  anticline  to  be  accessible.  There  is  no  direct  evidence  obtain- 
able on  either  of  these  questions  owing  to  the  complete  hiding  of  the 
oil-bearing  formations,  if  such  there  be,  by  the  great  thickness  of  over- 
lying  formations;  and  there  will  be  no  such  evidence  until  a test  is 
made  by  means  of  the  drill,  but  the  geologic  facts  observed  in  the 
hills  and  in  other  parts  of  the  district  afford  indirect  evidence  of  con- 
siderable importance  favoring  the  theory  that  the  necessary  condi- 
tions mentioned  above  do  exist. 

As  regards  the  first  condition,  it  may  be  reasonably  supposed  that 
the  Tejon  formation  underlies  the  whole  of  the  foothill  and  valley 
region  within  at  least  a few  miles  east  and  southeast  of  its  outcrop  in 
the  hills  around  Pleasant  Valley  and  along  Reef  Ridge.  There  is  no 
known  reason  for  supposing  otherwise.  The  San  Joaquin  Valley  has 
been  during  long  periods  of  geologic  time  a basin  of  depression  in 
which  deposition  of  sediments  and  subsidence  have  gone  on,  and  there 
is  evidence  to  show  that  during  the  Eocene,  when  the  Tejon  forma- 
tion was  being  deposited  in  the  sea  that  covered  part  of  the  area 
under  discussion,  the  present  Diablo  Range  was,  at  least  in  part,  a 
belt  of  land  that  stood  out  with  considerable  relief  and  formed  the 
shore  line.  The  sea  extended  thence  eastward,  and  unless  a belt  of 
land  rose  where  the  present  Kettleman  Hills  stand  the  formation 
must  have  been  deposited  over  their  area.  It  is  possible  that  the 
Coalinga  anticline  is  an  old  axis  of  uplift  that  may  have  determined 
an  area  of  relief  in  previous  epochs,  but  it  is  not  probable.  The  fact 
that  the  Cretaceous  beds  on  Joaquin  Ridge  are  not  more  disturbed 
than  the  younger  ones  lapping  over  the  anticline  farther  east  indi- 
cates that  no  great  uplift  occurred  along  this  anticline  before  the 
latest  period  of  movements,  during  which  all  of  the  formations  were 
affected  at  the  same  time. 

The  same  reasoning  applies  to  the  question  whether  the  Tejon  for- 
mation when  once  deposited  over  the  area  now  occupied  by  the 
Kettleman  Hills  was  worn  away  by  erosion  before  the  deposition  of 
the  younger  Tertiary  formations  and  the  preservation  in  them  of  the 
petroleum.  If  no  uplift  of  magnitude  occurred,  it  is  not. likely  that 
the  formation  was  worn  away.  In  fact,  it  was  probably  less  eroded 
than  in  the  region  farther  west,  where  it  is  now  exposed,  a region  that 
was  nearer  the  shore  line  and  more  subjected  to  disturbances.  It 


122 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


may  therefore  be  assumed  as  a good  working  hypothesis  that  the 
Tejon  was  originally  deposited  and  still  exists  beneath  the  forma- 
tions covering  the  surface  of  the  Kettleman  Hills.  Similarly  it  is  to 
be  supposed  that  the  whole  succession  of  Tertiary  formations  is  the 
same  beneath  these  hills  as  in  other  parts  of  the  district.  Whether 
or  not  the  Tejon  is  oil-bearing  can  not  be  told,  but  being  so  near  to 
the  extensive  area  in  which  it  is  petroliferous  the  chances  are  good 
that  it  is  likewise  so  beneath  these  hills. 

As  regards  the  second  condition,  the  evidence  afforded  by  the 
thickness  of  the  formations  in  various  parts  of  the  district  must  be 
brought  to  bear  in  order  to  determine  at  what  depth  the  oil-bearing 
beds  will  be  met.  The  anticline  exposes  along  its  axis  a low  portion 
of  the  Etchegoin  (uppermost  Miocene)  formation,  and  therefore  the 
drill  will  have  to  pierce  the  base  of  this  formation  and  the  whole  of 
the  Jacalitos  (early  upper  Miocene)  and  Santa  Margarita  (upper 
middle  Miocene)  formations  in  order  to  reach  the  petroliferous  beds 
of  the  Yaqueros  (lower  Miocene),  provided  that  these  formations  are 
present  as  they  have  been  assumed  to  be.  The  formations  here  prob- 
ably bear  a closer  similarity  in  occurrence  and  thickness  to  the  same 
formations  on  the  western  side  of  the  syncline  along  the  Kettleman 
Plain  than  they  do  to  the  formations  in  the  Coalinga  field.  The  oil 
probably  collects,  as  it  does  along  Reef  Ridge,  in  the  Vaqueros  sand- 
stone overlying  the  Tejon  (Eocene)  and  is  retarded  from  further 
upward  migration  by  the  compact  shales  of  the  Santa  Margarita. 

The  question  of  the  thickness  of  the  formations  may  be  taken  up 
with  relation  to  each  one  separately,  beginning  with  the  exposed 
Etchegoin.  This  formation  has  a thickness  of  approximately  3,500 
feet  throughout  the  Kreyenhagen  Hills,  of  which  about  2,700  is  below 
and  800  above  the  upper  Mulinia  zone.  On  Anticline  Ridge  the  for- 
mation has  a thickness,  only  roughly  measurable,  of  about  1,700  feet. 
In  the  Kettleman  Hills,  inasmuch  as  the  base  is  not  certainly  exposed, 
the  whole  formation  can  not  be  measured.  The  maximum  thickness 
exposed  is  about  3,000  feet  in  the  south-central  part  of  the  hills 
along  that  part  of  the  anticline  where  it  plunges  in  both  directions. 
Fossil  beds  are  there  exposed  which  may  be  close  to  the  base  of  the 
formation.  If  they  are,  the  whole  formation  is  thinner  than  in  the 
Kreyenhagen  Hills.  In  other  parts  of  the  Kettleman  Hills,  where  the 
lowest  beds  exposed  are  considerably  above  the  base,  the  only  means 
of  determining  the  comparative  thickness  of  the  formation  here  and 
elsewhere  is  to  compare  the  thickness  from  the  summit  down  to  the 
upper  Mulinia  zone,  which  has  been  correlated  with  a similar  zone  in 
the  Kreyenhagen  Hills.  This  thickness  is  about  1,900  to  2,000  feet 
in  the  northern  part  of  the  Kettleman  Hills,  but  increases  to  2,300  or 
2,400,  if  not  more,  in  the  southern  half,  on  the  southwest  flank  of  the 
anticline.  Here  again,  therefore,  there  is  indicated  a thinning  of  the 


THE  OIL  FIELDS. 


123 


formation  in  the  Kettleman  Hills,  as  compared  with  the  Kreyenhagen 
Hills,  and  this  gradual  decrease  appears  to  continue  on  the  north- 
eastern side  of  the  Kettleman  Hills.  On  the  other  hand,  there  is  a 
very  decided  thickening  southeastward  from  Anticline  Ridge  along 
the  anticline.  In  conclusion,  all  that  may  be  said  is  that  the  Etche- 
goin  is  at  least  2,000  feet  and  probably  more  nearly  2,500  feet  thick 
in  the  northern  part  of  the  Kettleman  Hills  and  at  least  3,000  feet 
thick  in  the  southern  part.  The  thickness  of  it  that  must  be  pierced 
along  the  axis  of  the  anticline  in  order  to  reach  the  underlying  Jaca- 
litos  decreases  gradually  southward  toward  the  central  portion  of  the 
hills.  At  the  south  side  of  sec.  34,  T.  21  S.,  R.  17  E.,  the  upper 
Mulinia  zone  arches  over  the  anticline  and  plunges  northwestward 
beneath  higher  beds.  At  this  point  the  beds  are  practically  horizontal 
on  the  very  axis  of  the  fold  and  the  depth  to  the  top  of  the  Jacalitos 
is  probably  only  a few  hundred  feet,  possibly  in  the  neighborhood  of 
500  feet.  From  there  southeastward  to  sec.  1,  T.  23  S.,  R.  18  E., 
the  thickening  of  the  formation  is  more  than  offset  by  the  plunge  of 
the  anticline  in  the  opposite  direction,  and  the  depth  to  the  Jacalitos 
gradually  decreases.  Thence  southward  the  depth  is  probably  no- 
where more  than  a few  hundred  feet  and  is  in  general  less  than  in  the 
northern  part  of  the  hills. 

The  Jacalitos  formation  has  a thickness  similar  to  that  of  the 
Etchegoin  both  in  the  Kreyenhagen  Hills  and  the  Coalinga  field. 
The  question  of  the  accessibility  of  the  oil  sand  in  the  Kettleman 
Hills  hinges  in  large  measure  on  the  question  whether  this  similarity 
in  thickness  between  the  two  formations  holds  good  there.  Does 
the  Jacalitos  become  thinner  eastward  from  the  Kreyenhagen  Hills, 
as  the  Etchegoin  seems  to  do?  It  is  very  probable  that  it  does. 

The  Santa  Margarita  increases  in  thickness  from  Zapato  Creek  to 
Dagany  Gap  from  about  200  feet  to  over  1,000  feet.  It  probably 
underlies  the  Kettleman  Hills  with  some  such  thickness  and  with  a 
probable  similar  thickening  southward.  There  is  no  way  of  telling 
whether  it  thickens  or  thins  eastward  from  the  Kreyenhagen  Hills, 
and  it  may  therefore  be  assumed  as  constant. 

On  the  basis  of  the  probable  conditions  outlined  above  the  com- 
bined thickness  of  the  lower  part  of  the  Etchegoin  below  the  upper 
Mulinia  zone  and  of  the  Jacalitos  and  Santa  Margarita  formations 
may  be  arbitrarily  assumed  to  be  3,500  feet  in  the  northern  part  of 
the  Kettleman  Hills  and  4,500  in  the  south-central  part.  The  lines 
on  the  map  over  the  Kettleman  Hills  showing  the  possible  limits  of 
the  productive  territory  are  drawn  on  the  basis  of  such  an  assump- 
tion. 

These  figures  are  moderate  estimates  and  the  chances  are  small 
that  the  thicknesses  are  less  than  this.  It  must  be  borne  in  mind, 
however,  that  they  are  at  best  only  guesses  based  on  a balance  of 


124  COALING  A OIL  DISTRICT,  CALIFORNIA. 

probabilities.  If  these  figures  be  true  it  means  that  the  top  of  the 
Vaqueros  formation,  the  supposed  oil  sand,  lies  between  3,500  and 
4,000  feet  immediately  below  the  axis  of  the  anticline  throughout 
the  hills  southeast  of  the  Big  Tar  Canyon-Lemoore  road.  Away 
from  the  axis  on  either  side  the  beds  begin  to  dip  away  and  the  depth 
do  the  Vaqueros  increases  rapidly.  The  lines  bounding  the  sup- 
posed oil  territory  represent  the  limits  of  the  area  in  which  the  top  of 
the  Vaqueros  would  be  reached  within  4,500  feet  vertically  down 
if  the  above- assumed  thicknesses  were  correct.  On  the  other  hand, 
if  the  formations  are  as  thick  as  they  are  in  the  Kreyenhagen  Hills, 
the  top  of  the  Vaqueros  would  be  considerably  below  4,500  feet  even 
along  the  axis  of  the  anticline.  In  the  southern  part  of  the  Kettle- 
man  Hills,  for  a few  miles  north  of  Avenal  Gap  and  in  the  group  south 
of  there,  the  structure  is  poorly  displayed.  Little  definite  informa- 
tion has  been  obtained  further  than  that  the  horizon  exposed  along 
the  axis  is  in  the  lower  portion  of  the  Etchegoin.  Owing  to  the  re- 
moval of  the  Eocene  by  faulting  near  Little  Tar  Canyon  and  south 
of  there  it  is  possible  that  the  Tejon  is  not  present  beneath  the  south- 
ern portion  of  the  Kettleman  Hills. 

No  surface  indications  of  oil  are  known  to  exist  in  the  Kettleman 
Hills,  but  it  is  not  likely  that  oil  would  have  been  allowed  to  escape 
through  the  great  thickness  of  overlying  beds  forming  the  regularly 
arching  anticline.  It  is  supposed,  also,  that  the  oil  is  retained  by  the 
overarching  shale  of  the  Santa  Margarita.  Indications  suggesting 
petroleum  have  been  observed  in  the  Lost  Hills  several  miles  south  of 
the  south  end  of  the  Kettleman  Hills.  The  Lost  Hills  may  be  due  to 
an  extension  of  the  Coalinga  anticline  southward,  and  it  is  possible 
that  the  fold  plunges  northward  and  exposes  a low  portion  of  the 
series  into  which  the  oil  has  had  access. 

In  conclusion,  it  may  be  said  that  the  Kettleman  Hills  offer  a fair 
chance  for  the  discovery  of  oil  at  a depth  of  from  3,000  to  4,500  feet 
along  the  axis  of  the  anticline,  and  that  the  conditions  favor  a well- 
preserved  supply.  The  only  possible  means  of  gaining  any  definite 
knowledge  of  the  oil-bearing  formations  beneath  these  hills  is  by 
drilling.  In  order  to  test  the  possibilities  of  the  region  satisfactorily 
wells  should  be  sunk  immediately  on  the  axis  of  the  anticline.  The 
most  favorable  location  for  a test  well  would  probably  be  between  the 
Big  Tar  Canyon-Lemoore  road  and  a point  13  miles  southeast  of 
the  northwest  end  of  the  hills. 

PRODUCTION. 

The  following  table  of  production  of  the  Coalinga  district  by  calen- 
dar years  from  1897  to  1907  was  compiled  by  Miss  Belle  Hill,  under 
the  direction  of  Dr.  David  T.  Day,  of  the  Geological  Survey.  The 
production  for  1908  will  probably  be  about  12,000,000  barrels, 


TRANSPORTATION  FACILITIES. 


125 


which,  with  the  greatly  increased  price  (63  to  75  cents  per  barrel), 
will  bring  the  value  of  the  product  for  the  year  close  to  $8,000,000. 


Production  of  Coalinga  district , 1897  to  1907. 


[In  barrels  of  42  gallons  each.] 


Year. 

Production. 

Value. 

1897 

70, 140 

154.000 
439, 372 

532. 000 
780,650 
572, 498 

1898 

1899 

1900 

$532, 000 
390,325 
257, 629 

1901  

1902 

1903 

1904 

1905 

1906 

1907 


Year. 

Production. 

Value. 

2, 138,058 
5, 114, 958 
10,967,015 
7,991,039 
8, 871, 723 

$705, 559 
1,520,847 
2, 657, 009 
1,848, 300 
3,091,934 

By"  a Fp&gli  estimate  based  on  the  data  in  the  hands  of  the  writers, 
the  amo^t  of  available  oil  contained  before  exploitation  began  in 
that  parfe^of  the  Coalinga  district  shown  on  the  contour  map  (PL  II) 
was  2,875,000,000  barrels  of  42  gallons  each.  Of  this  amount  about 

2.000. 000.000  barrels  was  contained  in  the  territory  west  of  the 
Coalinga  syncline  and  875,000,000  barrels  east  of  the  syncline.  The 
total  amount  taken  from  the  ground  up  to  the  present  time,  includ- 
ing an  estimated  production  of  12,000,000  barrels  for  1908,  approaches 

50.000. 000  barrels,  which,  when  subtracted  from  the  estimated 
total,  leaves  2,825,000,000  barrels  available  after  1908.  At  the  pres- 
ent rate  of  production  this  supply  would  last  over  200  years,  but  with 
the  rapid  rate  at  which  the  increase  in  production  is  now  taking  place 
the  time  during  which  the  supply  will  hold  out  promises  to  be  far  less. 
Moreover,  it  is  not  possible  to  state  what  percentage  of  the  oil  present 
can  ultimately  be  obtained. 

The  estimate  is,  of  course,  merely  an  approximation.  It  was 
arrived  at  by  assuming  a 10  per  cent  impregnation  of  the  oil  sands 
and  calculating  from  all  the  data  available  the  probable  thickness 
of  sand  under  each  quarter  section. 

TRANSPORTATION  FACILITIES. 

One  railroad  and  two  pipe  lines  comprise  the  transportation  facil- 
ities for  the  oil  produced  in  the  Coalinga  district. 

A branch  of  the  Southern  Pacific  Railroad  joins  Coalinga  with  the 
main  lines  at  Hanford  and  Goshen  Junction,  and  also  with  the  main 
lines  of  the  Atchison,  Topeka  and  Santa  Fe  Railway  at  Hanford 
and  Visalia.  The  storage  tanks  and  loading  racks  for  the  district 
are  at  Ora  station,  1J  miles  northeast  of  Coalinga. 

A 6-inch  pipe  line  of  the  Coalinga  Oil  Transportation  Company,  a 
subsidiary  of  the  Associated  Oil  Company,  joins  Coalinga  with  the 
seaboard  at  Monterey,  110  miles  northwest.  This  line  was  first 
constructed  in  1904  as  an  independent  project,  and  was  generally 
known,  from  the  name  of  its  projector,  as  the  Matson  pipe  line.  The 


126 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


route  traversed  is  along  Alcalde  Canyon,  Waltham  Valley,  Priest 
Valley,  Lewis  Creek,  and  the  Salinas  Valley.  Several  pumping  sta- 
tions are  situated  along  the  line  between  Coalinga  and  Monterey, 
the  main  pumping  station  being  located  in  the  SW.  4 sec.  18,  T.  20  S., 
R.  15  E. ; it  is  joined  by  minor  lines  with  various  parts  of  the  Eastside 
and  Westside  fields. 

An  8-inch  branch  pipe  line,  28  miles  long,  joins  the  Coalinga  field 
with  the  main’  Kern  River-Point  Richmond  line  of  the  Standard 
Oil  Company  at  Mendota.  The  total  distance  from  Coalinga  to 
tidewater  by  this  line  is  198  miles.  The  main  pumping  station  of 
this  company  for  the  Coalinga  field  is  in  the  NW.  4 sec.  36,  T.  19  S., 
R.  15  E. 

Numerous  local  lines  transport  the  oil  from  various  parts  of  the 
field  to  the  shipping  stations.  Among  these  lines  are  those  of  the 
Union  Oil  Company  from  sec.  13,  T.  20  S.,  R.  14  E.,  to  Ora;  the 
California  Oilfields,  Ltd.,  from  the  Eastside  field  to  Ora;  the  Coalinga 
Oil  Company,  from  the  Oil  City  field  to  Ora;  Westside  line,  from  the 
Westside  field  to  Ora,  and  the  Associated  Oil  Company,  from  the 
Westside  field  to  Ora. 

MINERAL  LANbs. 

The  following  areas  within  the  Coalinga  district  have  been  classified 
as  mineral  lands,  and  such  of  these  as  yet  belong  to  the  Government 
have  been  withdrawn  from  any  but  mineral-land  entry.  The  lands 
classified  as  mineral  include  all  those  lying  between  the  outcrop  of 
the  lowest  oil-bearing  formations,  the  Tejon  (Eocene),  and  a line 
marking  the  limits  of  the  area  in  which  the  uppermost  productive 
oil  zone  (zone  B),  can  be  reached  by  a well  less  than  4,500  feet  in 
depth.  (See  pp.  113-114  for  relative  probability  of  productiveness  of 
these  lands.) 

List  of  mineral  lands  in  Coalinga  district. 

T.  18  S.,  R.  15  E.: 

W.  | and  SE.  4 sec.  36,  secs.  35,  U,  and  33. 

T.  19  S.,  R.  14  E.: 

S.  | and  NE.  4 sec.  25,  S.  \ sec.  35,  and  sec.  36. 

T.  19  S.,  R.  15  E.: 

Secs.  1 to  4,  8 to  17,  SE.  4 sec.  18,  and  secs.  19  to  36  except  NW.  4 sec.  19. 

T.  19  S.,  R.  16  E.: 

W.  | secs.  7,  18,  19,  and  30,  and  all  of  sec.  31. 

T.  20  S.,  R.  14  E.: 

Secs.  1 to  3,  10  to  15,  22  to  26,  35,  and  36. 

T.  20  S.,  R.  15  E.: 

All  of  township  except  secs.  23,  26,  35,  36,  SW.  4 sec.  14,  E.  4 sec.  27,  N.  4 and 
NE.  4 sec.  25. 

T.  20  S.,  R.  16  E.: 

W.  \ sec.  5,  secs.  6,  7,  8,  SW.  4 sec.  9,  secs.  16  to  21,  W.  \ sec.  22,  secs.  27  to  30, 
NE.  4 sec.  31,  secs,  32  to  33,  and  W.  4 sec.  34. 


OIL  COMPANIES  AND  OIL  WELLS. 


127 


T.  21  S.,  R.  14  E.: 

Sec.  1,  E.  \ sec.  2,  sec.  12,  N.  \ and  SE.  \ sec.  13. 

T.  21  S.,  R.  15  E.  : 

Secs.  2 to  9,  N.  \ sec.  10,  NW.  i sec.  11,  S.  \ sec.  16,  secs.  17,  18,  21,  22,  NW.  i 
and  S.  \ sec.  23,  secs.  26,  27,  E.  \ sec.  28,  N.  \ and  SE.  \ sec.  34,  and  W.  \ sec. 
35. 

T.  21  S.,  R.  16  E.: 

N.  \ sec.  3 and  NE.  \ sec.  4. 

T.  21  S.,  R.  17  E.: 

Secs.  33,  34,  and  NW.  \ and  S.  \ sec.  35. 

T.  22  S.,  R.  15  E.: 

SW.  \ sec.  5,  S.  \ sec.  6,  secs.  7,  8,  NW.  \ and  S.  \ sec.  9,  SW.  \ sec.  10,  SW.  \ 
sec.  13,  NW.  i and  S.  \ sec.  14,  secs.  15,  16,  N.  \ sec.  17,  N.  \ sec.  18,  NW.  | 
sec.  22,  NW.  \ and  E.  \ sec.  23,  secs.  24,  25,  and  NE.  ^ sec.  26. 

T.  22  S.,  R.  16  E.: 

NW.  i and  S.  ^ sec.  19,  SW.  \ sec.  20,  SW.  \ sec.  27,  NW.  \ and  S.  \ sec.  28,  secs. 
29,  30,  N.  \ sec.  31,  secs.  32  to  34,  and  SW.  \ sec.  35. 

T.  22  S.,  R.  17  E.: 

NW.  i and  S.  \ sec.  1,  secs.  2,  3,  E.  \ sec.  4,  NW.  i and  E.  \ sec.  10,  secs.  11,  12, 
NW.  1 and  E.  \ sec.  13,  and  NE.  \ sec.  14. 

T.  22  S.,  R.  18  E.: 

Sec.  7,  NW.  \ and  S.  | sec.  8,  NW.  \ and  S.  \ sec.  16,  secs.  17,  18,  N.  | sec.  19, 
secs.  20,  21,  22,  SW.  \ sec.  25,  secs.  26,  27,  28,  NE.  £ sec.  29,  NE.  £ sec.  33, 
and  secs.  34,  35,  and  36. 

T.  23  S.,  R.  16  E.: 

S.  \ sec.  1,  secs.  2,  3,  4,  N.  \ sec.  10,  secs.  11,  12,  and  N.  \ sec.  13. 

T.  23  S.,  R.  17  E.: 

Sec.  7,  S.  \ sec.  8,  SW.  i sec.  15,  NW.  \ and  S.  \ sec.  16,  sec.  17,  NW.  \ and  E.  \ 
sec.  18,  N.  \ sec.  20,  secs.  21,  22,  SW.  \ sec.  23,  SW.  J sec.  25,  sec.  26,  N.  \ 
and  SE.  Jsec.  27,  NE.  £ sec.  35,  and  sec.  36. 

T.  23  S.,  R.  18  E.: 

Secs.  1,  2,  NE.  \ sec.  3,  E.  \ sec.  11,  secs.  12, 13,  N.  \ and  SE.  \ sec.  24,  NE.  ^ sec. 
25,  and  SW.  \ sec.  31. 

T.  23  S.,  R.  19  E.: 

W.  \ sec.  6,  secs.  7,  18,  19,  W.  \ sec.  20,  SW.  i sec.  28,  secs.  29,  30,  E.  | sec.  31, 
secs.  32,  33,  and  SW.  \ sec.  34. 

T.  24  S.,  R.  18  E.: 

SW.  \ sec.  5,  secs.  6,  7,  NW.  \ and  S.  \ sec.  9,  SW.  \ sec.  15,  sec.  16,  N.  £ and  SE.  | 
sec.  17,  N.  \ and  SE.  £ sec.  21,  NW.  \ and  S.  \ sec.  22,  sec.  27,  E.  \ sec.  28, 
sec.  34,  and  W.  | sec.  35. 

T.  24  S.,  R.  19  E.: 

Secs.  3,  4,  N.  \ and  SE.  \ sec.  5,  secs.  9,  10,  15,  16,  21,  22,  SW.  \ sec.  26,  secs.  27, 
28,  N.  \ and  SE.  \ sec.  33,  sec.  34,  and  NW.  \ and  S.  \ sec.  35. 

OIL  COMPANIES  AND  OIL  WELLS  IN  THE  COALINGA 

DISTRICT. 

The  following  is  a practically  complete  list  of  all  of  the  oil  compa- 
nies which  have  drilled  or  are  drilling  wells  in  the  Coalinga  district. 
The  locations  of  the  wells  are  indicated  wherever  known  and  the  ele- 
vation of  each  well  given  in  most  instances,  having  been  obtained  by 
instrument  survey  by  E.  P.  Davis,  topographer.  There  are  now  395 


128 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 

productive  wells,  75  abandoned  wells,  and  between  75  and  100  drilling 
wells  in  the  district. 

Oil  companies  and  oil  wells  in  Coalinga  district. 

[Location  by  Mount  Diablo  base  and  meridian.] 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

iEtna.  (See  California  Oil- 

fields,  Ltd.) 

j Feet. 

Ajax 

# 

a 1 

SW.  \ sec.  32,  T.  19  S.,  R.  15  E 

b 2 

Sec.  30,  T.  20  S.,  R.  15  E 

1 

NE.  i sec.  26,  T.  20  S.,  R.  14  E. 

840 

~Do 

2 

do.. 

842 

Arline.  (See  California  Oil- 

fields,  Ltd.) 

1 

SW.  \ sec.  22,  T.  19  S.,  R.  15  E. 

1,255 

Do 

2 

do 

1,235 

Do 

3 

do 

1,223 

Do 

4 

do 

l’  208 

Do 

5 

do 

1,144 

Do 

Sauer  Dough  No.  1 

1 

do 

1,435 

Do 

Sauer  Dough  No.  2. . . 

2 

do 

1,304 

Do 

Sauer  Dough  No.  3 

3 

do. . . 

1,313 

Do 

Sauer  Dough  No.  4. . . 

4 

do. . . 

1,388 

Do 

Sauer  Dough  No.  5. . . 

5 

do 

1,435 

Do 

Sauer  Dough  No.  6. . . 

6 

do. . 

1,283 

Do 

Sauer  Dough  No.  7 . . . 

7 

. . .do 

1,340 

Do  

1 

SE.  \ sec.  36,  T.  20  S.,  R.  14  E. 

835 

Do 

2 

do 

875 

Do 

3 

do 

831 

Do 

4 

do 

934 

Do 

5 

do 

828 

Do 

21 

NE.  J sec.  36,  T.  20  S.,  R.  14  E. 

800 

Do ! 

23 

do. 

814 

Do  1 

25 

do. . . 

828 

Do 

27 

NW.  I sec.  36,  T.  20  S.,  R.  14  E. 

843 

Do  

29 

.do 

858 

A venal  Land  and  Oil__ 

a 2 

Sec.  18,  T.  23  S.,  R.  17  E 

Avon.  (See  California  Oil- 

fields, Ltd.) 

B and  B 

Brix  and  Buntin 

1 

SE.  \ sec.  12,  T.  20  S.,  R.  14  E. 

848 

Do  

2 

.do 

852 

Baby  Xing  ‘ 

a 1 

NE.  a sec.  11,  T.  23  S. , R.  16  E . 

Badger  State  j 

a 1 

Sec.  1,  T.  21  S.,  R.  14  E. 

Black  Mountain  ; 

a 2 

NW.|  sec.  33,  T.  22  S.,R.  16  E. 

Blair .... ' 

b 1 

NW.  a sec.  14,  T.  21  S.,  R.  15  E. . 

Blue  Diamond 

a 1 

NE.  I sec.  26,  T.  20  S.,  R.  14  E. 

920 

Blue  Goose  

a 1 

NE.  | sec.  20,  T.  19  S.,  R.  15  E. 

Bonanza  King 

a 1 

SW.  a sec.  10,  T.  19  S.,  R.  15  E. 

Boston  and  California 



b 1 

SE.  i sec.  24,  T.  19  S.,  R.  15  E. 

Buena  Vista  {Kettleman 



Hills). 

Buntin.  (See  California  Dia- 

mond.) 

Caledonian 

1 

NE.  \ sec.  26,  T.  20  S.,  R.  14  E. 

882 

Do 

a 2 

. . . .do 

880 

Do  

3 

do 

847 

Do 

4 

.do 

842 

California  and  New  York 

1 

SE.a  sec.  12,  T.  20  S.,  R.  14  E. 

834 

Do 

2 

. do  

848 

Do 

3 

do 

829 

Do ! 

4 

do 

835 

Do 

5 

do 

843 

California  Diamond 

1 

SW.  A sec.  12,  T.  19  S.,  R.  15  E. 

802 

Do j 

Ellis,  No.  1 1 

3 

NE.  a sec.  31,  T.  19  S.,  R.  15  E. 

1,192 

Do 

4 

..  ..do 

1,196 

Do. . . 

Buntin  No  1 

a 1 

NW.  J sec.  24,  T.  21  S.,  R.  15  E. 

California  Monarch 

1 

SE.  i sec.  26,  T.  19  S.,  R.  15  E . 

954 

Do.. . 

b 2 

do 

889 

California,  Oil  and  Ga,s  . . 

a 1 

SE.  a sec.  19,  T.  19  S.,  R.  15  E. 

California  Oilfields,  Ltd 

Avon,  No.  1 

1 

SW.  i sec.  14,  T.  19  S.,R  15E. 

1,101 

Do 

Avon,  No.  2 

2 

NW.  a sec.  14,  T.  19  S.,  R.  15  E . 

1,035 

Do 

Kaweah,  No.  1 

3 

NE.  a sec.  14,  T.  19  S.,  R.  15  E. 

877 

Do 

Kaweah,  No.  2 

4 

SE.  a sec.  14,  T.  19  S.,  R.  15  E. 

950 

Do 

Avon,  No.  3 

b 5 

NW.  i sec.  14,  T.  19  S.,  R.  15  E. 

856 

Do 1 

1 

SE.  ] sec.  21,  T.  19  S.,  R.  15  E. 

1,451 

Do.. . 

2 

.do 

1,322 

Do 

3 

do 

1,444 

Do 1 

4 

do 

1,340 

a Abandoned. 


£>  Drilling. 


OIL  COMPANIES  AND  OIL  WELLS. 

Oil  companies  and  oil  wells  in  Coalinga  district  Continued. 


129 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 



5 

SE.  \ sec.  21,  T.  19  S.,  R.  15  E. 

Feet. 

1,429 

6 

do 

1,461 



7 

do 

1,377 

Do 

8 

1,383- 

Do 

9 

NE.  \ sec.  21,  T.  19  S.,  R.  15  E. 

1,368 

Do 

Arline,  No.  1 

1 

SW.  i sec.  26,  T.  19  S.,  R.  15  E. 

1,007 

Do 

Arline,  No.  2 

2 

NW.  \ sec.  26,  T.  19  S.,  R.  15  E. 

1,028 

Do 

Northeastern,  No.  1 . . 

3 

NE.  i sec.  26,  T.  19  S.,  R.  15  E. 

950 

Do  

1 

NW.l  sec. 27, T.  19  S.,R.  15  E. 

1,387 

Do 

2 

do 

1,363 

Do 

3 

do 

1,349 

1,353 

Do 

4 

do 

Do 

5 

do 

1,380 

Do 

6 

do 

1,214 

Do 

7 

I do 

1,331 

Do 

8 

1,305 

Do 

9 

1 do 

« 1,319 

Do 

10 

do 

« 1,080 

Do 

11 

I do 

« 1,340 

Do 

12 

1 SW.  J sec.  27,  T.  19  S.,  R.  15  E. 

a 1,284 

Do 

13 

NW.  i sec.  27,  T.  19  S.,  R.  15  E. 

« 1,130 

Do 

14 

do 

a 1,270 

Do 

15 

do 

a 1,225 

Do 

16 

do 

« 1,229 

Do 

17 

l do 

1,332 

1,340 

1,256 

Do 

18 

1 do 

Do 

19 

1 SW.  i sec.  27,  T.  19  S„  R.  15  E. 

Do 

20 

i do : 

1,307 

1,117 

Do 

21 

do 

Do 

22 

do 

1,144 

Do 

23 

SE.  \ sec.  27,  T.  19  S.,  R.  15  E. 

1,105 

Do 

24 

SW.  i sec.  27.  T.  19  S.,  R.  15  E. 
do 

1,238 

Do 

25 

1,246 

Do 

26 

NW.  \ sec.  27,  T.  19  S.,  R.  15  E. 
SE.  } sec.  27,  T.  19  S.,  R.  15  E. 
NW.  \ sec.  27,  T.  19  S.,  R.  15  E. 
do 

1,273 

Do 

b 27 

983 

Do 

28 

1,257 

Do... 

29 

1,188 

Do... 

30 

do 

a 1,275 
1,194 

Do 

31 

SW  i sec.  27,  T.  19  S.,  R.  15  E. 
do 

Do 

32 

1,166 

1,260 

Do 

33 

do 

Do 

6 34 

i NE.  i sec.  27,  T.  19  S.,  R.  15  E. 
i NW.  i sec.  27,  T.  19  S.,  R.  15  E. 
NE.  i sec.  27.  T.  19  S.,  R.  15  E. 

1,022 

1,168 

Do 

35 

Do 

36 

a 1,180 

Do 

37 

! SW.  i sec.  27,  T.  19  S.,  R.  15  E. 
do 

1,271 
1,234 
1,225 
a 1,350 
1,217 
1,256 
1,225 
1,118 
1,096 
1, 109 

Do 

38 

Do 

39 

..  ..do 

Do. 

41 

NW.  \ sec.  27,  T.  19  S.,  R.  15  E. 
SW.  i sec.  29,  T.  19  S.,  R.  15  E. 
do 

Do 

1 

Do 

2 

Do 

TEtna,  No.  1 

1 

SE.  i sec.  30,  T.  19  S.,  R.  15  E. . 
NW  \ sec.  34,  T.  19  S.,  R.  15  E. 

Do 

Westmoreland,  No.  1. 

' 1 

Do 

Forty,  No  1 

2 

NE.  i sec.  34,  T.  19  S.,  R.  15  E. 

Do 

Westmoreland,  No.  2. 
Missouri  Coalinga, 
No.  1. 

Westmoreland,  No,  3. 

3 

NW.  \ sec.  34,  T.  19  S.,  R.  15  E. 

Do 

4 

.do 

1,150 

Do 

5 

.do... 

1,085 

1,061 

Do 

Forty,  No.  3 

Pittsburg  - Coalinga, 
No.  1. 

6 

NE.  1 sec.  34,  T.  19  S.,  R.  15  E. 
do 

Do 

7 

1,080 

Call 

1 

NW.isec.32,T.  19S.,  R.  15  E. 

1,213 

Caribou  Oil  Mining 

1 

SW.  i sec.  22,  T.  19  S.,  R.  15  E. 
.do . . 

1,399 

1.356 

1.357 
1,417 
1,391 

Do 

2 

Do 

3 

do . . . 

Do 

4 

. .do  . 

Do 

5 

. . do . . . 

Do 

6 

. .do . . , 

1,400 
1 1,297 

1,234 
1,204 
1,233 
1,313 
1,116 

Do. 

7 

. .do. . . 

Do 

8 

. .do . . . 

Do ! 

9 

.do . . . 

Do 

10 

do. . 

Do 

11 

. .do . . . 

Do 

12 

do . . 

Do...  

6 13 

do . . 

1,309 

Carmel  ita 

rl 

SE.  Jsec.  3,  T.  20S..R.  15  E.. 
NE  l sec  35  T 20  S R 14  E 

Circle 

6 1 

Claremont 

1 

NW.  | sec.  24,  T.  20  S.’  R.  14  E. 
do 

a 810 
a 814 

Do 

2 

a Approximate. 

52332— Bull.  357—08 9 


6 Drilling. 


c Abandoned. 


130 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 

Oil  companies  and  oil  wells  in  Coaling  a district — Continued. 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

Claremont 

3 

NW.  1 sec.  24,  T.  20  S.,  R.  14  E .1 
.do. 

Feet. 

« 805 

Do 

4 

792 

Do 

61 

NE.  i sec.  4,  T.  20  S.,  R.  15  E. 
NW.  J sec.  20,  T.  19  S.,  R.  15  E . 

.do 

1,022 
a 1,405 

1,453 

Coalinga 

Producers  and  Con- 
sumers, No.  1. 

c 1 

Do 

2 

Do 

c 2. 

do 

a 1,410 

Do 

sumers,  No.  2. 

3 

.do .... 

1,453 

1,421 

Do 

3 

.do 

Do 

sumers,  No.  3. 

4 

do 

1,449 

1,465 

Do 

5 

do 

Do 

6 

. do .... 

1,435 

1,579 

1,499 

Do 

7 

do 

Do 

9 

do 

Coalinga  Four 

Sec.  4,  T.  20  S.,  R.  15  E 

Coalinga  Mohawk 

b 1 

NW.  \ sec.  12,  T.  20  S.,  R.  15  E. 

o 850 

Coalinga  Pacific 

1 

NW.  | sec.  7,  T.  20  S.,  R.  15  E .1 
do 1 

880 

Dck 

2 

883 

Do 

3 

do 

910 

Do 

4 

do ] 

873 

Coalinga-Peerless 

1 

NW.  i sec.  22,  T.  19  S.,  R.  15  E. 

1,362 

Do". 

2 

do 

1,284 

Do 

3 

...do ! 

1,363 

Do. . . 

4 

do 

1,360 

1,260 

1,259 

1,261 

Do. . . 

5 

do 

Do. . . 

6 

. .do 

Do 

7 

do 

Do 

8 

do 

1,212 

1,224 

Do 

9 

do 

Do 

10 

do 

1,168 

Do 

11 

do 

1,259 

Do. . . 

12 

do 

1,150 

Coalinga  Petroleum ....  * . 

1 

NE.  \ sec.  14,  T.  20  S.,  R.  14  E. 
do 

870 

Do 

2 

878 

Do 

3 

do 

887 

Do 

4 

do 

883 

Coalinga  Southern 

| 

61 

NW.  \ sec.  6,  T.  21  S.,  R.  15  E . 

920 

Coalinga  Western 

1 

NE.  I sec.  23,  T.  20  S.,  R.  14  E. 

968 

Do 

2 

do 

977 

Do... 

3 

do 

960 

Do.. . 

4 

do 

910 

Do  .. 

5 

do 

887 

Do 

(?)« 

(7)7 

1 

do 

960 

Do 

. . . .do 

869 

Coast  Range .... 

SW.  i sec.  17,  T.  19  S.,  R.  15  E. 

a 1,450 

Do 

2 

do 

a 1,450 

Do 

3 

do 

1,451 

Do 

4 

SE.  J sec.  17,  T.  19  S.,  R.  15  E. 

1, 469 

Do 

5 

SW.  I sec.  17,  T.  19  S.,  R.  15  E . 

1,485 

Do. 

6 

do 

1,533 

| 

Commercial 

c2 

SE.  J sec.  12,  T.  21  S.,  R.  14  E. 

Commercial  Petroleum 

1 

do 

869 

Do 

1 

NE.  J sec.  31,  T.  19  S.,  R.  15  E. 
do 

1,236 

Do 

2 

1,243 

Do 

3 

do 

1,242 

Do 

4 

do 

1,253 

Do 

5 

do 

1,244 

Do 

6 

....do 

1,241 

Do 

7 

do 

1,259 

Do  . 

8 

do : 

1,254 

Do  .. 

9 

do 

1,239 

Do  . 

10 

do 

1,220 

Confidence..  .. 

2 

NW.  \ sec.  31,  T.  19  S.,  R.  15  E . 

a 1,280 

Do 

4 

do 

a 1,275 

Do 

5 

SW.i  sec.  31,  T.  19  S.,  R.  15  E. 

■1,101 

Do 

6 

NW . \ sec.  31,  T.  19  S.,  R.  15  E . 

1,240 

Do. . . 

7 

do 

1,236 

Do 

8 

SW.  £ sec.  31,  T.  19  S.,  R.  15  E. 

1,251 

Do 

9 

do 

1,190 

Do 

10 

do 

1,227 

Do  . 

11 

do 

1,171 

Do 

K and  C No.  5 

12 

do 

1,203 

Do 

6 13 

do 

1,205 

Do 

6 14 

do 

1,243 

Consolidated  Oil  and  De- 

c, 

NE.  1 sec.  10,  T.  23  S.,  R.  16  E. 

velopment. 

« Approximate. 


b Drilling. 


c Abandoned. 


OIL  COMPANIES  AND  OIL  WELLS. 


131 


Oil  companies  and  oil  wells  in  Coalinga  district — Continued. 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location.  ~ 

Eleva- 
tion 
above 
mean 
sea  level. 

ai 

SE.  \ sec.  20,  T.  19  S.,  R.  15  E . 

Feet. 

R.  H.  Herron,  No.  1. . 
R.  H.  Herron,  No.  2.. 

1 

SE.  i sec.  1,  T.  20  S.,  R.  14  E . . 

917 

'"Do  . 

2 

911 

Do 

3 

do 

941 

Do 

R.  H.  Herron,  No.  4. . 

4 

do 

738 

NE.  \ sec.  35,  T.  18  S.,  R.  15  E. 

El  Capitan  (now  Kern  Trad- 
ing and  Oil). 

2 

NW.  \ sec.  31,  T.  19  S.,  R.  15  E . 

b 1 

NW.  \ sec.  14,  T.  23  S.,  R.  17  E. 

Elk 

a 1 

NE.  \ sec.  22,  T.  19  S.,  R.  15  E. 

Ellis.  (See  California  Dia- 
mond.) 

Esperanza  Oil  and  Gas 

1 

SW.  i sec.  6,  T.  20  S.,  R.  15  E. 

. 997 

" Do 

2 

do 

989 

Do. . . 

3 

do 

972 

Do 

4 

do 

956 

Do 

5 

do 

981 

Do 

6 

do 

943 

Do 

b 7 

do 

936 

Do 

8 

do 

916 

Do 

a 2 

SW.  \ sec.  14,  T.  22  S.,  R.  17  E. 

b 1 

Sec.  30,  T.  21  S.,  R.  15  E 

Euclid 

1 

SW.i  sec.  24,  T.  20  S.,R.  14  E. 

814 

Do 

2 

do 

824 

Fauna 

a 1 

NW.  i sec.  28,  T.  19  S.,  R.  15  E . 

o2 

NW.  i sec.  15,  T.  22  S.,  R.  17  E . 

Forty.  (See  California  Oil- 
field, Ltd.) 

Fresno-San  Francisco 

1 

NE.  i sec.  1,  T.  20  S.,R.  14  E. 
.do 

1,140 

Do... 

2 

1,128 

1,072 

Do 

3 

do 

Do  .. 

4 

.do 

.1,114 

Gibbs 

a 1 

NW.  i sec.  28,  T.  21  S.,  R.  17  E . 

Golden  Crest. 

Kreyenhagen,  No.  1 . . 

b\ 

NE.  1 sec.  12,  T.  22  S.,  R.  15  E . 

Golden  State  (now  California 
Oilfields,  Ltd.). 

Graham,  W.  M 

a 1 

SE.  \ sec.  30,  T.  19  S.,  R.  15  E . 

1 

NE.'i  sec.  6,  T.  21  S.,  R.  15  E. 

759 

Do 

1 

Sec.  2,  T.  19  S.,  R.  15  E 

Great  Western 

a 1 

SW.  I sec.  26,  T.  19  S.,  R.  15  E . 

Guthrey 

1 

NE.  1 sec.  31,  T.  19  S.,  R.  15  E . . 

1,267 

1,263 

Do 

2 

do 

Do 

3 

do 

1,227 

1,242 

1,356 

Do 

4 

do 

Guthrey.  (See Yellowstone.) 
Hanford 

1 

NW.  1 sec.  28,  T.  19  S.,  R.  15  E . 
do 

Do 

2 

1,379 

1,404 

Do 

3 

.do 

Do 

4 

do  .. 

1,385 

1,376 

Do 

5 

SW.  i sec.  28,  T.  19  S.,  R.  15  E. . 
NW.  i sec.  28,  T.  19  S.,  R.  15  E . 

Do 

6 

1,387 

1,469 

1,341 

Do 

7 

do 

Do 

8 

SW.  I sec.  28,  T.  19  S.,  R.  15  E. . 
Sec.  6,  T.  21?  S.,  15?  E 

Hawkeye  State 

a 2 

Henshaw.  (See  Sunny  side.) 
Herron,  R.  H.  (See  Cypress.) 
Highland 

New  York,  Nos.  1 

a 2 

SW.  i sec.  20,  T.  19  S.,  R.  15  E. . 

Home 

and  2. 

1 

NE.  I sec.  20,  T.  19  S„  R.  15  E . . 
. . .do 

c 1 , 490 

Do 

2 

1,491 

Do 

3 

. .do 

1,567 

Do 

4 

.do. . . 

1,528 

Do 

5 

.do.  . 

1,597 

Do..  

6 

.do . . . 

1,519 

Do 

7 

.do. . 

1,585 

1,593 

Do 

8 

do. 

Inca 

1 

NW.  1 sec.  24,  T.  20  S.,  R.  14  E . 
. .do .... 

801 

Do 

2 

811 

Do 

3 

do 

816 

Do 

4 

do.  . 

799 

Do 

5 

.do . . . 

814 

Do 

6 

.do . 

805 

Do 

7 

do 

797 

Do 

8 

do  . 

805 

Do 

9 

do 

814 

Do 

10 

do 

818 

Do 

11 

do 

834 

Do 

12 

do 

870 

Imperial 

61 

1 Sec.  2,  T.  19  S.,  R.  15  E 

a Abandoned . t Drilling.  c Approximate. 


132 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Oil  companies  and  oil  wells  in  Coalinga  district — Continued. 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well,  j 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

Independence.  (See  Stand- 
ard.) 

Independent 

a 1 

NE.  i sec.  17,  T.  19  S , R.  15  E 

Feet. 

Investment 

a 1 

SE.  \ sec.  16,  T.  19  S.,  R.  15  E 

Iowa 

a ] 

SW.  \ sec.  4,  T.  22  S.,  R.  17  F 

Jacalitos 

b 1 

Sec.  30,  T.  21  S.,  R.  15  E 

K.  and  C.  (See  Confidence.) 
Kaweah.  (See  California  Oil- 
fields, Ltd.) 

Kern  Trading  and  Oil 

b 1 

NW.  4 sec.  35,  T.  19  S.,  R.  15  E . 

Do r 

1 

SW'. | sec. 31,  T.  19 S.,  R.  15 E. . 

*c*i,2i6 

1,234 

1,222 

1,270 

1,242 

811 

Do 

2 

do 

Do 

3 

N W.  1 sec.  31,  T.  19  S.,  R.  15 E . 
do 

Do 

7 

Do 

8 

do 

Do 

1 

SW.  4 sec. 25,  T.20S.,  R.14E.. 

Do 

2 

.do 

803 

Keystone 

a 1 

NW.  4 sec.  32,  T.  19  S.,  R.  15  E 

Kings  County 

a 1 

NE.  \ sec.  3,  T.  23  S.,  R.  16  E 

Do r 

a 1 

SW.  1 sec.  3,  T.  23  S.,  R.  16  E... 

a 2 

SE.  4 sec.  32,  T.  22  S.,  R.  16  E... 

Kreyenhagen.  (See  Golden 
Crest.) 

Lorene 

b 1 

N W.  i sec.  12.  T.  19  S.,  R.  15 E . 
NE.  4 sec.  6,  T.  21  S.,  R.  15  E . . . 

c 825 

Lucile 

1 

770 

Do 

2 

do 

761 

McCreary.  (See  California 
Oilfields,  Ltd.) 

Maine  State 

1 

NE.4  sec.  31,  T.  19 S.,  R.  15E.. 

1,256 
cl,  300 

Do 

a 2 

do 

Do 

3 

do 

1,274 
1,237 
c 1,250 
1,089 
1,119 
1,119 

Do 

4 

. .do 

Do.. 

5 

.do. . . . 

Do 

6 

SE.  3 sec.  31,  T.  19  S.,  R.  15E... 
do 

Do 

7 

Do 

8 

do 

Do... 

9 

do 

1,154 

900 

Manchester 

a 1 

SW.  i sec.  18,  T.  21  S..  R.  15  E. . 
S W.  1 sec.  24,  T.  20  S.,  R.  14  E. . 

Marengo 

1 

c 790 

Do  . 

2 

do 

c800 

Do 

3 

.do 

c 795 

Do.. 

b 4 

do 

c 795 

May  Brothers 

a 1 

SE.  i sec.  14,  T.  20  S.,  R.  14  E.. . 

Mercantile  Crude 

1 

N W.  \ sec.  6,  T.  20  S.,  R.  15  E.  . 
do 

1,097 

Do.. 



2 

cl,  120 

Do 

3 

do 

1,006 

Do 

4 

do 

1,002 

Michigan  Oil  and  Develop- 
ment. 

Minnesota  (now  Southern 
Pacific  R.  R.) 

Missouri-Coalinga.  (See  Cali- 
fornia Oilfields,  Ltd.) 

M.,  K.  and  T 

b 1 

Sec.  17?,  T.  19  S.,  R.13E 

a 2 

NE.  4 sec.  33,  T.  19  S.,  R.  15  E . . 

1 

SW.  4 sec.  8.  T.  20  S.,  R.  15  E.. . 

868 

Do 

b 2 

. . . .do 

866 

Montjack 

a 1 

NW.  4 sec.  22,  T.  19  S.,  R.  15  E . 

Mount  Hamilton  Land  and 

a 1 

SE.  4 sec.  14,  T.  21  S.,  R.  14  E... 
SE.  4 sec.  20,  T.  19  S.,  R.  15  E... 

1,002 

Oil. 

Mutual 

a 1 

Nathan.  (See  Porter  & 

Scribner.) 

New  Era 

1 

SE.  4 sec.  12,  T.  20  S.,  R.  14  E... 

New  Home 

1 

SE.  4 sec.  14,  T.  20  S.,  R.  14  E... 

736 

Do 

2 

do 

746 

Do 

3 

do 

737 

New  San  Francisco  Crude. 

1 

NW.  4 sec.  6,  T.  20  S.,  R.  15  E.  . 

1,135 

Do 

2 

do 

1,105 

Do 

3 

do 

1,068 

Do 

4 

do 

1,098 

Do 

5 

do 

1,079 

New  York.  (See  Highland.) 
Norse 

1 

S W.  4 sec.  24,  T.  20  S..  R.  14  E. . 

Do 

1 b 2 

do 

Do 

! b 3 

do 

Do 

4 

do 

Northeastern.  (See  Califor- 
nia Oilfields,  Ltd.) 

a Abandoned. 

b Drilling. 

c Approximate. 

OIL  COMPANIES  AND  OIL  WELLS, 


133 


Oil  companies  and  oil  wells  in  Coalinga  district — Continued. 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

Feet. 

Oceanic 

a 1 

NW.  i sec.  1,  T.  22  S.,  R.  17  E . . 

Octave 

1 

NE.isec.22,  T.  19S.,  R.  15E.. 

1,212 

Do 

2 

do 

1,208 

Oil  City  Petroleum.  (See 

Standard.) 

Old  Keystone 

° 1 

SE.isec.8,  T.  19S.,  R.  15E... . 

Oyama.  (See  California  Oil- 

fields,  Ltd.) 

1 | 

NE.  \ sec.  26,  T.  20  S.,  R.  14  E . . 

b 850 

Do 

2 

do 

b 845 

cl 

NE.  sec.  10,  T.20S.,  R.15E  ... 

815 

cl 

Sec.  24,  T.20S.,  R.14E 

1 

NE.  1 sec.  24,  T.20S.,  R.14E.. 

1, 056 

Do 

2 

SE.  i sec.  24,  T.  20  S.,  R.  14  E . . 

976 

Do 

3 

do 

923 

Do 

4 1 

do 

975 

Philadelphia  and  San  Fran- 

l ! 

SE.  isec.  36,  T.  19S.,R.  14  E. 

1,121 

cisco. 

l 

Do 

2 

do 

Do 

3 j 

do 

1,107 

a 3 

SE.  I sec.  20,  T.  19  S.,  R.  15  E. 

1 

SW.  1 sec.  12,  T.  20  S.,  R.  14  E. 



1 

SW.  \ sec.  24,  T.  19  S.,  R.  15  E. 

830 

Pittsburg-Coalinga.  (SeeCal- 

ifornia  Oilfields,  Ltd.) 

1 

NW.  \ sec.  7,  T.  20  S.,  R.  15  E. 

873 

Do  

do 

a 2 

do 

868 

Do  .. 

do 

3 

. . .do 

848 

1 

SE.  I sec.  24,  T.  20  S.,  R.  14  E. 

b 790 

Do  

2 

do 

Producers  and  Consumers. 

(See  Coalinga.) 

Record 

1 

SE.  | sec.  22,  T.  19  S.,  R.  15  E. 

1,189 

Do  . 

2 

! do 

1,177 

Riverside  (near  Alcalde). 

• 

Roanoke 

a 1 

SE.  \ sec.  36,  T.  19  S.,  R.  14  E . 

Rock 

a 1 

SW.  | sec.  28,  T.  19  S.,  R.  15  E 

St.  Clair 

1 

SW.  i sec.  12,  T.  20  S.,  R.  14  E 

St.  Francis 

c 1 

SW.  J sec.  6,  T.  21  S.,  R.  15  E. 

b 940 

St.  Lawrence 

a 1 

NE.  \ sec,  12  T.  23  S.  R.16F.. 

St.  Paul-Fresno 

1 

NE.  J see.  23,  T.  20  S.,  R.  14  E. 

b 950 

Do 

2 

do 

970 

Do... 

3 

! ..  do 

920 

Do 

4 

906 

Do 



5 

1 do 

910 

Santa  Clara 

a 1 

1 SW.  i sec.  30  T.  19  S.  R.  15  E 

Sauer  Dough.  (See  Asso- 

1 

ciated.  1 

Section  Seven 

1 

i NW.  J sec.  7,  T.  20 S.,  R.  15  E. 

911 

Do 

2 

1 do 

915 

Do 



3 

do 

916 

Do 

4 

1 do 

908 

Do 

c5 

do 

b 880 

Section  Six 

cl 

NW . i sec.  6,  T.  21  S.,  R.  15  E . 

842 

Section  Ten  

o,l 

SW.  Jsec.  10,  T.  19  S.,  R.  15  E 

Selma.  (See  Zenith.) 

Seneca 

cl 

NW.  I sec.  12,  T.  20  S.,  R.  14  E . 

Shawmut 

1 

NE.  I sec.  12,  T.  20  S.,  R.  14  E . 

878 

Do 

2 

. do 

882 

Do 

3 

do 

892 

Do 

4 

do . . . 

b 910 

Do 

5 

do 

879 

Shreeve 

1 

NW.  \ sec.  6,  T.  21  S.,  R.  15  E 

853 

Standard 

Independence,  No.  1 . . 

1 

NE.  I sec.  28,  T.  19  S.,  R.  15  E. 

1,497 

Do 

Independence,  No.  3.. 

3 

do 

1,440 

Do 

Independence,  No.  4. . 

4 

do 

1,374 

Do 

Independence,  No.  5. . 

5 

do 

51,450 

Do 

Independence,  No.  6. . 

6 

do 

1,444 

Do 

Independence,  No.  7. . 

7 

do 

1,458 

Do 

Independence,  No.  8.. 

8 

do 

1,484 

Do 

Independence,  No.  9.. 

9 

do . 

1,536 

Do 

Independence,  No.  10. 

10 

do 

1,538 

Do 

Oil  City  Petroleum, 

11 

SE.  \ sec.  28,  T.  19  S.,  R.  15  E. 

1,371 

No.  1. 

Do 

Oil  City  Petroleum, 

12 

do 

1,404 

No.  2. 

Do. 

Oil  City  Petroleum, 

13 

«do 

1,372 

No.  3. 

a Abandoned. 

b Approximate 

c Drilling. 

134 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 

Oil  companies  and  oil  wells  in  Coalinga  district — Continued. 


Name  of  oil  company. 

Name  of  well. 

No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

Feet. 

Standard 

Oil  City  Petroleum, 

14 

SE.  i sec.  28,  T.  19  S.,  R.  15  E . . 

1,376 

No.  4. 

Do 

15 

do 

1,448 

No.  5." 

Do 

16 

do. 

1,373 

No.  6“ 

Do 

17 

do 

1,348 

No.  7. 

Do 

18 

do 

1,340 

No.  8." 

Do 

Oil  City  Petroleum, 

19 

• do 

1,361 

No.  9. 

Do 

20 

do 

1,321 

No.  10. 

Do 

Oil  City  Petroleum, 

21 

do 

1,323 

No.  11. 

Do 

22 

do. . . . 

1,262 

No.  12. 

Do 

23 

do .... 

1,211 

No.  13. 

Do 

24 

do. . 

1,253 

No.  14. 

Do 

25 

do . 

1,275 

No.  15. 

Do 

Twenty-eight,  No.  14. 

26 

NE.  1 sec.  28,  T.  19  S.,  R.  15  E. 

1,314 

Do 

27 

do 

1,395 

Do 

28 

do 

1*385 

Do 

29 

do 

1*241 

Do 

30 

. .do . . . 

1*378 

Do 

Twenty-eight,  No.  9. . 

31 

do 

1*420 

Do. 

Twenty-eight,  No.  8. . 

32 

do 

1*402 

Do 

Twenty-eight,  No.  6. . 

33 

do 

1*  256 

Do 

Twenty-eight,  No.  5. . 

34 

do 

1*342 

Do 

Twenty-eight,  No.  4. . 

35 

. do . . . 

1*342 

Do 

Twenty-eight,  No.  1.. 

36 

. . .do 

a 1*380 

Do 

Twenty-eight,  No.  3.. 

37 

do' 

1,364 

Do 

Twenty-eight,  No.  2. . 

38 

do . . . 

1*  428 

Do 

Twenty-eight,  No.  7.. 

39 

do . . . 

1*  421 

Do 

Twenty-eight,  No.  15. 

40 

do 

1*  456 

Do 

Twenty-eight,  No.  16. 

41 

.do 

1,505 

Stanislaus 

b 1 

NW.  \ sec.  4,  T.  22  S.  R.  17  E. 

Star 

b 1 

NW.  I sec.  34  T.  19  S.  R.  15  E. 

Stockholders 

1 

NE.  J sec.  28  19  S.  R.  15  E. 

1,486 

Do 

2 

do 

l’  385 

Do 

3 

do 

P 394 

Do 

4 

do 

1,407 

Do 

5 

do 

1,454 

Stockton 

b 2 

NW.  | sec.  30  T.  22 S.,  R.  18  E. 

Sunnyside 

Henshaw 

c 1 

SE.  J sec.  35  T.  20  S.,  R.  14  E. 

S.  W.  and  B 

1 

NW.  | sec.  6'  T.  20  S.,  R.  15  E. 

1,061 

Do 

2 

do 

1,038 

Do 

3 

. .do 

1,031 

Do 

4 

do 

982 

Tavern 

d 1 

Sec.  34  T.  18  S.  R.  15  E... 

T.  C 

1 

SW.  \ sec.  2,  T.  19  S.,  R.  15  E. 

958 

Traders 

1 

SW.  Jsec.  24,  T.  20 S.’,  R.  14  E. 

810 

Do 

2 

..  . do 

818 

Do 

3 

do 

845 

Do 

4 

. . .do 

833 

Do 

5 

do 

a 843 

Twenty-eight.  (See  Stand- 

ard.) 

Twenty-two 

1 

SE.  \ sec.  22,  T.  19  S.,  R.  15  E. 

1,143 

Turner 

d 1 

SW.  \ sec.  2,  T.  20  S.,  R.  15  E. 

a 1,075 

Do 

d 2 

do 

a 975 

Union 

1 

N W . \ sec.  13,  T.  20  S.,  R.  14  E . 

812 

Do 

2 

NE.i  sec.  13,  T.  20  S.,  R.  14  E . 

811 

Do 

3 

.do 

810 

Do 

4 

NW . \ sec.  13,  T.  20  S.,  R.  14  E. 

817 

Do 

5 

do 

808 

Do 

6 

do 

824 

Do 

7 

do 

817 

Do 1... 

8 

do 

837 

Do , 

9 

..do. . . 

835 

Venus 

b 1 

NW . I sec.  5,  T.  22  S.,  R.  14  E.i 

a Approximate.  b Abandoned.  c "Water  well.  d Drilling. 


OIL  COMPANIES  AND  OIL  WELLS, 


135 


Oil  companies  and  oil  wells  in  Coalinga  district — Continued. 


Name  of  oil  company. 

Name  of  well. 

|No.  of 
well. 

Location. 

Eleva- 
tion 
above 
mean 
sea  level. 

1 

2 

3 

1 

6 

! 8 
9 

10 

11 

12 

1 

2 

1 

a 3 
a 1 

O 1 
a 1 
1 
2 
b 3 
a 1 
1 
1 
2 
a 2 
1 1 
2 ! 

?! 

5 ! 

6 ! 

7 1 

NE.  \ sec.  24,  T.  20  S.,  R.  14  E. 
do 

Feet. 

806 

802 

798 

793 

789 

787 

782 
796 

783 
779 

in 

775 

933 

934 
1,052 

Do. . . 

Do. . . 

do 

Do 

do 

Do 

do 

do 

Do 

do 

Do 

' do 

Do 

i do 

Do 

do 

Do 

do 

Do 

do 

Ward 

NW.  \ sec.  12,  T.  20  S.,  R.  14  E . 
do 

Do 

West  Coalinga  (water) 

NE.  i sec.  12,  T.  21  S.,  R.  14  E . i 
NE.  \ sec.  2,  T.  21  S.,  R.  14  E. 

Sec.  4,  T.  22  S.,  R.  14  E 1 

W estlake-Rommel 

Westmoreland.  (See  Califor- 
nia Oilfields,  Ltd.) 

Whale 

King 

Whittier  and  Green 

NW.  I sec.  26,  T.  20  S.,  R.  14  E . ! 

Wisconsin 

NE.  Jsec.  32,  T.  19  S.,  R.  15  E. 

W.  K 

NW.  i sec.  2,  T.  20  S.,  R.  15  E. 
do 

920 

1,125 

c960 

Do 

Do 

NE.  a sec.  2.T.20S..R.  15E. 
NW.  a see.  26,  T.  20  S.,  R.  14  E . 

Wright  Association 

:::::::::::::::::::::::: 

Yellowstone 

Guthrey,  No.  1 

NW.  a sec.  6,  T.  21S.,R.15E. 
NW.  | sec.  G,  T.  20  S.,  R.  15  E. 
do 

917 

1,123 

1,085 

* ' ’ '939 

938 
964 
970 
945 

939 
953 

York  Coalinga 

Do 

Zenith 

Selma,  Nos.  1 and  2. . . 

! SE.  I sec.  20,  T.  19  S„  R.  15  E. 
SW.  a sec.  1,  T.  20  S.,  R.  14  E. 
do 

Zier 

Do 

Do . . 

do 

Do... 

do .... 

Do 

do 

Do 

do 

Do 

do . . . 

* 

a Abandoned.  Drilling.  c Apr -oximate. 


SURVEY  PUBLICATIONS  ON  PETROLEUM  AND  NATURAL 

GAS. 


The  following  list  includes  the  more  important  papers  relative  to 
oil  and  gas  published  by  the  United  States  Geological  Survey  or  by 
members  of  its  staff.  Those  to  which  a price  is  affixed  can  be -pur- 
chased from  the  Superintendent  of  Documents,  Government  Printing 
Office,  Washington,  D.  C.  Any  of  the  others  (published  by  the 
Survey)  can  be  had  free  by  applying  to  the  Director,  U.  S.  Geological 
Survey,  Washington,  D.  C. 

Adams,  G.  I.  Oil  and  gas  fields  of  the  western  interior  and  northern  Texas  coal 
measures  and  of  the  Upper  Cretaceous  and  Tertiary  of  the  western  Gulf  coast.  In 
Bulletin  No.  184,  pp.  1-64.  1901. 

Adams,  G.  I.,  Haworth,  E.,  and  Crane,  W.  It.  Economic  geology  of  the  Iola 
quadrangle,  Kansas.  Bulletin  No.  238.  83  pp.  1904. 

Anderson,  R.  (See  Arnold,  R.,  and  Anderson,  R.) 

Arnold,  R.  The  Salt  Lake  oil  field,  near  Los  Angeles,  Cal.  In  Bulletin  No.  285, 
pp.  357-361.  1906. 

—  Geology  and  oil  resources  of  the  Summerland  district,  Santa  Barbara  County, 

Cal.  Bulletin  No.  321.  67  pp.  1907. 

The  Miner  ranch  oil  field,  Contra  Costa  County,  Cal.  In  Bulletin  No.  340, 

pp.  339-342.  1908. 

(See  also  Eldridge,  G.  H.,  and  Arnold,  R.) 

Arnold,  R.,  and  Anderson,  R.  Preliminary  report  on  the  Santa  Maria  oil  district, 
Santa  Barbara  County,  Cal.  Bulletin  No.  317.  69  pp.  1907. 

—  — - — — Geology  and  oil  resources  of  the  Santa  Maria  oil  district,  Santa 

Barbara  County,  Cal.  Bulletin  No.  322.  161  pp.  1907.  50c. 

Boutwell,  J.  M.  Oil  and  asphalt  prospects  in  Salt  Lake  basin,  Utah.  In  Bulletin 
No.  260,  pp.  468-479.  1905.  40c. 

Clapp,  F.  G.  The  Nineveh  and  Gordon  oil  sands  in  western  Greene  County,  Pa. 
In  Bulletin  No.  285,  pp.  362-366.  1906. 

—  (See  also  Stone,  R.  W.,  and  Clapp,  F.  G.) 

Crane,  W.  R.  (See  Adams,  G.  I.,  Haworth,  E.,  and  Crane,  W.  R.) 

Eldridge,  G.  Ii.  The  Florence  oil  field,  Colorado.  In  Trans.  Am.  Inst.  Min.  Eng., 
vol.  20,  pp.  442-462.  1892. 

The  petroleum  fields  of  California.  In  Bulletin  No.  213,  pp.  306-321. 

1903.  25c. 

Eldridge,  G.  H.,  and  Arnold,  R.  The  Santa  Clara  Valley,  Puente  Hills,  and 
Los  Angeles  oil  districts,  southern  California.  Bulletin  No.  309.  266  pp.  1907. 

Fenneman,  N.  M.  The  Boulder,  Colo.,  oil  field.  In  Bulletin  No.  213,  pp.  322-332. 
1903.  25c. 


136 


SURVEY  PUBLICATIONS  ON  PETROLEUM  AND  NATURAL  GAS.  137 


Fenneman,  N.  M.  Structure  of  the  Boulder  oil  field,  Colorado,  with  records  for 
the  year  1903.  In  Bulletin  No.  225,  pp.  383-391.  1904.  35c. 

The  Florence,  Colo. , oil  field.  In  Bulletin  No.  260,  pp.  436-440.  1905.  40c. 

Oil  fields  of  the  Texas-Louisiana  Gulf  coast.  In  Bulletin  No.  260,  pp. 

459-467.  1905.  40c. 

Oil  fields  of  the  Texas-Louisiana  Gulf  coastal  plain.  Bulletin  No.  282.  146 

pp.  1906. 

Fuller,  M.  L.  The  Gaines  oil  field  in  northern  Pennsylvania.  In  Twenty-second 
Ann.  Rept.,  pt.  3,  pp.  573-627.  1902.  $2. 

Asphalt,  oil,  and  gas  in  southwestern  Indiana.  In  Bulletin  No.  213,  pp. 

333-335.  1903.  25c. 

The  Hynergas  pool,  Clinton  County,  Pa.  In  Bulletin  No.  225,  pp.  392-395. 

1904.  35c. 

Griswold,  W.  T.  The  Berea  grit  oil  sand  in  the  Cadiz  quadrangle,  Ohio.  Bulletin 
No.  198.  43  pp.  1902. 

Structural  work  during  1901-2  in  the  eastern  Ohio  oil  fields.  In  Bulletin 

No.  213,  pp.  336-344.  1903.  25c. 

Petroleum.  In  Mineral  Resources  U.  S.  for  1906,  pp.  827-896.  1907. 

Structure  of  the  Berea  oil  sand  in  the  Flushing  quadrangle,  Ohio.  Bulletin 

No.  346.  30  pp.  1908. 

Griswold,  W.  T.,  and  Munn,  M.  J.  Geology  of  oil  and  gas  fields  in  Steubenville, 
Burgettstown,  and  Claysville  quadrangles,  Ohio,  West  Virginia,  and  Pennsylvania. 
Bulletin  No.  318.  196  pp.  1907. 

Haworth,  E.  (See  Adams,  G.  I.,  Haworth,  E.,  and  Crane,  W.  R.;  also  Schrader, 
F.  C.,  and  Haworth,  E.) 

Hayes,  C.  W.  Oil  fields  of  the  Texas-Louisiana  Gulf  coastal  plain.  In  Bulletin 
No.  213,  pp.  345-352.  1903.  25c. 

Hayes,  C.  W.,  and  Kennedy,  W.  Oil  fields  of  the  Texas-Louisiana  Gulf  coastal 
plain.  Bulletin  No.  212.  174  pp.  1903.  20c. 

Hill,  B.  Natural  gas.  In  Mineral  Resources  U.  S.  for  1906,  pp.  811-826.  1907. 

Kennedy,  W.  (See  Hayes,  C.  W.,  and  Kennedy,  W.) 

Kindle,  E.  M.  Salt  and  other  resources  of  the  Watkins  Glen  quadrangle,  New  York. 
In  Bulletin  No.  260,  pp.  567-572.  1905.  40c. 

McGee,  W J.  Origin,  constitution,  and  distribution  of  rock  gas  and  related  bitu- 
mens. In  Eleventh  Ann.  Rept.,  pt.  1,  pp.  589-616.  1891. 

(See  also  Phinney,  A.  J.) 

Munn,  M.  J.  (See  Griswold,  W.  T.,  and  Munn,  M.  J.) 

Oliphant,  F.  H.  Petroleum.  In  Nineteenth  Ann.  Rept.,  pt.  6,  pp.  1-166.  1898. 

Petroleum.  In  Mineral  Resources  U.  S.  for  1903,  pp.  635-718.  1904.  70c. 

Idem  for  1904,  pp.  675-759.  1905. 

Natural  gas.  In  Mineral  Resources  U.  S.  for  1903,  pp.  719-743.  1904.  70c. 

Idem  for  1904,  pp.  761-788.  1905. 

Orton,  E.  The  Trenton  limestone  as  a source  of  petroleum  and  inflammable  gas 
in  Ohio  and  Indiana.  In  Eighth  Ann.  Rept.,  pt.  2,  pp.  475-662.  1889.  $1.50. 

Phinney,  A.  J.  The  natural  gas  field  of  Indiana,  with  an  introduction  by  W J 
McGee  on  rock  gas  and  related  bitumens.  In  Eleventh  Ann.  Rept.,  pt.  1,  pp.  579-742. 
1891. 

Richardson,  G.  B.  Natural  gas  near  Salt  Lake  City,  Utah.  In  Bulletin  No.  260, 
pp.  480-483.  1905.  40c. 

Salt,  gypsum,  and  petroleum  in  trans-Pecos  Texas.  In  Bulletin  No.  260, 

pp.  573-585.  1905.  40c. 

Petroleum  in  southern  Utah.  In  Bulletin  No.  340,  pp.  343-347.  1908. 


188 


COALINGA  OIL  DISTRICT,  CALIFORNIA. 


Schrader,  F.  C.,  and  Haworth,  E.  Oil  and  gas  of  the  Independence  quadrangle, 
Kansas.  In  Bulletin  No.  260,  pp.  442-458.  1905.  40c. 

Schultz,  A.  R.  The  Labarge  oil  field,  central  Uinta  County,  Wyo.  In  Bulletin 
No.  340,  pp.  364-373.  1908. 

Shaler,  M.  K.  (See  Taff,  J.  A.,  and  Shaler,  M.  K.) 

Stone,  R.  W.  Oil  and  gas  fields  of  eastern  Greene  County,  Pa.  In  Bulletin  No. 
225,  pp.  396-412.  1904.  35c. 

Mineral  resources  of  the  Elders  Ridge  quadrangle,  Pennsylvania.  Bulletin 

No.  256.  86  pp.  1905. 

Stone,  R.  W.,  and  Clapp,  F.  G.  Oil  and  gas  fields  of  Greene  County,  Pa.  Bulletin 
No.  304.  110  pp.  1907. 

Taff,  J.  A.,  and  Shaler,  M.  K.  Notes  on  the  geology  of  the  Muscogee  oil  fields, 
Indian  Territory.  In  Bulletin  No.  260,  pp.  441-445.  1905.  40c. 

Washburne,  C.  W.  Gas  fields  of  the  Bighorn  Basin,  Wyoming.  In  Bulletin  No. 
340,  pp.  348-363.  1908. 

Weeks,  J.  D.  Natural  gas  in  1894.  In  Sixteenth  Ann.  Rept.,  pt.  4,  pp.  405-429. 
1895.  $1.20. 

Willis,  Bailey.  Oil  of  the  northern  Rocky  Mountains.  In  Eng.  and  Min.  Jour., 
vol.  72,  pp.  782-784.  1901. 


INDEX. 


A.  Page. 

Acknowledgments  to  those  aiding 9-10 

Alcalde  Canyon,  definition  of . . . 15 

rocks  of 41 

structure  of 66 

Alcalde  Hills,  definition  of 14 

rocks  of  and  near 33-34, 45-46, 48 

Anderson,  F.  M.,  names  given  by 40, 46 

Anticlinal  theory,  statement  of 70 

Anticline  Canyon,  section  at 101-102 

Anticline  Ridge,  definition  of 13 

oil  in 116-117  j 

Area,  extent  of 7 i 

Associated-Caledonian-Union  area,  location 

of 96 

production  of 98 

wells  of 96-98 

log  of 98 

Avenal  Gap,  definition  of 15  I 

sections  near 59-60  J 

Avenal  Land  and  Oil  Co.,  well  of 110  I 

well  of,  log  of 110 

Avenal  Ridge,  definition  of 14 

Avenal  syncline,  description  of 67 

B. 

Baby  King  Oil  Co.,  well  of 109-110 

Bibliography  of  petroleum  and  gas 136-138 

Big  Blue  sand,  character  and  distribution  of.  30, 
32, 33, 36-37, 79-80, 82-83, 84, 86, 88, 100 
See  also  particular  fields,  areas,  etc. 

Big  Sulphur  water,  occurrence  and  character 

of * 72 

Big  Tar  Canyon,  rocks  near 44 

sections  in  and  near 35, 38, 51-52 

Black  Mountain  Oil  Co.,  well  of 110-111 

well  of.  log  of 110 

Blue  Goose  Oil  Co.,  well  of 78 

C. 


Caledonian  area.  See  Associated,  etc.,  area. 
California,  southern,  map  of,  showing  oil  ter- 
ritory   9 

California  Diamond  area.  See  Peerless,  etc., 
area. 

alifomia  Monarch  area  See  Standard-Cari- 


bou, etc.,  area. 

California  Oil  and  Gas  Co.,  well  of 78 

California  Oilfields — Coalinga-  Mohawk  area, 

location  of 86 

production  of 87 

wells  of 86-87 


See  also  Standard-Califomia  Oil  fieldsarea. 


Page. 

Call-Confidence  area,  location  of 89 

production  of 91 

wells  of 89-91 

Canoas  Canyon,  definition  of 16 

Canoas  Creek,  sections  on 35,43,51 

Caribou  area.  See  Standard-Caribou,  etc., 
area. 

Castle  Mountain,  fault  zone  at 66-67 

Chico  rocks.  See  Knoxville-Chico. 

Coalinga  anticline,  location  and  character  of.  64-65 

section  on 54 

Coalinga  area.  See  California  Oilfields,  etc., 
area. 

Coalinga  district,  definition  of 12 

Coalinga  field,  definition  of 12 

rocks  of 36-37,48-49 

Coalinga  Oil  Transportation  Co.,  pipe  line 

of 125-126 

Coalinga  syncline,  location  and  character  of.  65 

Commercial  Petroleum  Co.,  well  of,  section 

near 104 

Confidence  area.  See  Call-Confidence  area. 
Consolidated  Oil  and  Development  Co.,  well 

of 109 

Contours,  structure,  use  of 74-75 

Cooperation,  advantages  of 10-11 

Crescent  Oil  Co.,  well  of 78 

Cretaceous  rocks,  character  and  distribution 

of 21-23 

Curry  Mountain,  description  of. 17-18 

D. 

Dagany  Gap,  definition  of 15 

Diablo  anticline,  description  of 67 

Diablo  Range,  definition  of 12-13 

description  of 16-17 

rocks  of 41,61-62 

structure  of 62 

Diastrophism,  description  of 62-63 

E. 

Eastside  field,  future  development  in 115-116 

northwest  of,  future  development  in. . . 114-115 


See  also  Peerless-Califomia  Diamond-T. 
C.  area;  Standard-Car  ibou-Cali- 
fomia  Monarch  area;  Standard- 
Califomia  Oilfields  area;  Califor- 
nia Oilfields-Coalinga-Mohawk 
area;  Standard  - Stockholders  - 
Hanford  area. 


El  Cerito  Oil  Co.,  well  of Ill 

Eldridge,  G.  H.,  work  of 7-8 


139 


140 


INDEX, 


Page. 

Eocene  rocks,  character  and  distribution  of. . 27-29 

Esperanza  Oil  Co.,  well  of 113 

Etchegoin  formation,  character  and  distribu- 
tion of 29-31, 

46-56,  86,  88,  89,  91,  93,  96, 
99, 101-102, 105,  111,  122-123 

oil  and  relation  of 55 

sections  of 51-52,54-55 

F. 

Fairbanks,  H.  W.,  formation  named  by 57 

Faults  and  folds,  occurrence  and  character  of.  63, 

67-68, 102-104 

Florence  Oil  Co.,  well  of 113 

Franciscan  formation,  character  and  distri- 


bution of 20-21 

igneous  rocks  in 61-62 

relation  of,  to  oil 21 


Folds.  See  Faults  and  folds;  Structure. 

G. 

Garza  Creek,  rocks  near 44 

Gas,  bibliography  of. 136-138 

occurrence  and  character  of 82,84 

Geography,  description  of 11-16 

Geology,  account  of 19-68 

See  also  Stratigraphy;  Structure;  Igneous 
rocks;  'particvlar  areas,  fields,  etc. 

Gibbs  Oil  Co.,  well  of 112 

Glycymeris  zone,  character  and  distribution 

of 30,45-46,47 

Guijarral  Hills,  definition  of 15 

oil  in 116-117 

rocks  of 60-61 

H. 

Hanford  area.  See  Standard-Stockholders, 
etc.,  area. 

I. 


Page. 

Juniper  Ridge,  definition  of 13-14 

description  of 17-18 

J urassic  rocks,  character  and  distribution  of. . 20-21 

K. 

Kettleman  Hills  definition  of 15 

description  of. 17 

oil  in 116-117,120-124 

rocks  of 52-60 

sections  in 54-55 

structure  of. 65 

Kettleman  Hills  field,  definition  of 12, 111-112 

geology  of H2 

oil  in H2 

wells  of. 112-113 

Kettleman  Plain,  definition  of 15 

rocks  of 56 

structure  of 65 

Kings  County  Oil  Co.,  well  of 109,111 

well  of,  log  of ill 

Knoxville-Chico  rocks,  character  and  dis- 
tribution of 21-23,99-102,105-108 

relation  of,  to  oil 23 

Kreyenhagen  field,  definition  of 12 

geology  of 37-40, 108 

location  of 107 

oil  of 108 

wells  of 108-111 

logs  of 110,111 

Kreyenhagen  Hills,  definition  of 14 

rocks  of 40-41,50-52,60 

L. 

Laval  grade,  definition  of 16 

Location  of  district 7,11-12 

Los  Gatos  basin,  structure  of 65-66 

Los  Gatos  Creek,  description  of 19 

rocks  near 25 

Lost  Hills,  oil  in 124 

M. 


Igneous  rocks,  description  and  distribution 


of 61-62 

Indicator  bed,  character  and  distribution  of. . 33 

Iowa  Oil  Co.,  well  of 113 


J. 


Jacalitos  anticline,  oil  in 118-119 

Jacalitos  Creek,  rocks  of 41-42 

section  of 42 

Jacalitos  formation,  character  and  distribu- 
tion of 29-31,  40-46,  79,  82, 

84,  86,  91,  93,  96,  99, 100, 105,  108, 123. 

oil  and,  relation  of 46,70 

sections  of 42,43 

Jacalitos  Hills,  definition  of 14 

rocks  of  and  near 34,41-43,60 

structure  of. 66 

Jacalitos  zones,  occurrence  and  character  of. . 70 

Jasper  Creek,  definition  of 16 

rocks  in 39 

Joaquin  Ridge,  definition  of 13 

description  of 17 

rocks  of 29 

structure  of 64-65 


McLure  Valley,  definition  of 15 

rocks  in 39 , 41 , 44, 52 

Map,  geologic,  of  Coalinga  district Pocket 

Map,  index,  of  southern  California 9 

Map,  structure-contour,  of  Coalinga  district.  Pocket 

accuracy  of 75-76 

preparation  and  use  of 74-75 

Mercantile  Crude — S.  W.  & B.  area,  location 

of 91 

production  of 93 

wells  of 91-93 

log  of 93 

Mineral  lands,  list  of 126-127 


Miocene  rocks,  character  and  distribution  of.  29-31 
See  also  Vaqueros;  Santa  Margarita;  Ja- 
calitos; Etchegoin. 

M.  K.  & T.  area.  See  Zier,  etc.,  area. 

Mohawk  area.  See  California  Oilfields,  etc., 
area. 

Mulinia  zone,  character  and  distribution  of. . 50 

My  a zone,  character  and  distribution  of 50,53 

O. 

Oceanic  Oil  Co.,  well  of 112 

Oil,  accumulation  of 70-71,113-114 


INDEX, 


141 


Page. 

Ofi,  bibliography  of 136-138 

character  of 7 

future  development  of 113-124 

gravity  of 71  > 

79, 81,83-84, 85, 87, 88-89, 91,93, 95,98 

occurrence  of 68-71 

origin  of 7>7^ 

relation  of,  to  formations 21  > 

23,28-29,35,40,46,55,61 

to  water 72 

yield  of 7>  124-125 

See  also  particular  areas,  fields,  etc. 

OU  areas,  location  of,  map  showing 9 

Oil  Canyon,  location  of 16 

rocks  at 37 

Oil  City  field,  geology  of 76-77 

location  of 76 

production  of 78-79 

wefis  of 77-78 

logs  of 77,78 

Oil  companies,  list  of 127-135 

Oil  fields,  descriptions  of 76 

future  development  of 113-124 

map  of , description  of 74-76 

subdivisions  of 74  j 

See  also  particular  fields. 

Oil  wefis,  list  of 127-135 

Oil  zones,  character  and  distribution  of 68-70 

See  also  particular  areas,  wells  of. 

Oil  zones  A,  B.  See  Jacalitos  zones. 

B,  C,  D.  See  Vaqueros  zones. 

Operators,  cooperation  among 10-11 


P. 


Paso  Robles  formation,  character  and  distri- 


bution of 56-61,111 

oil  and,  relations  of 61 

sections  of 59-60 

Pecten  coalingensis  zone,  character  and  distri- 
bution of 50,53 

Peerless-Califomia  Diamond-T.  C.  area,  loca- 
tion of 79 

production  of 81-82 

wefis  of 79-81 

water  of 82 

Phoenix  Oil  Co.,  well  of,  log  of 78 

Pipe  lines,  description  of 125-126 

Place  names,  definitions 12-16 

Pleasant  Valley,  definition  of 15 

rocks  in  and  near 24-25, 32-33, 37, 41, 46 

structure  of 65 

Pleistocene  deposits,  character  and  distribu- 
tion of 29-31, 61 


Pliocene  rocks,  character  and  distribution  of.  29-31, 

56-61 


Polvadero  Gap,  definition  of 15 

Porter  & Scriber  area.  See  Zier,  etc.,  area. 

Pulaski  sand,  occurrence  and  character  of 81 

Pyramid  Hills,  definition  of 14 

rocks  of 37,38,39 

Pyramid  Hills  anticline,  description  of 67 


R.  Page. 


Railroads,  access  by 7, 12, 125 

Reef  beds,  character  and  distribution  of 31-32 

Reef  Ridge,  definition  of 14 

description  of 18 

oil  in 119-120 

rocks  of  and  near . . . 25-27, 29-30, 31, 34, 35, 37-39 

section  of 35 

Report,  plan  of 7-8 

Roads,  location  of 12 

S. 

St.  Lawrence  Oil  Co.,  well  of Ill 

St.  Paul  sand,  occurrence  and  character  of.  „ . 84 

San  Joaquin  Valley  coal  mine  area.  See  Wal- 
tham Creek,  etc.,  area. 

Santa  Margarita  formation,  character  and  dis- 
tribution of 29-31, 

35-40, 79, 82, 84, 100,110,123 

oil  and,  relations  of 40,70 

section  of 38 

Santa  Margarita  zone,  occurrence  and  charac- 
ter of 70 

Sauer  Dough  sand,  occurrence  and  character 

of. 81 

Sec.  2,  T.  21  S.,  R.  14  E.,  area,  production  of.  107 

wefis  of 106-107 

Selma  Oil  Co.,  well  of 78 

Standard-Califomia  Oilfields  area,  location  of.  84 

production  of 85-86 

wells  of 84-85 

Standard-Caribou-California  Monarch  area, 

location  of 82 

production  of 83-84 

wefis  of 82-83 

Standard  Ofi  Co.,  pipe  line  of 126 

Standard-Stockholders-Hanford  area,  location 

of. 87 

production  of 88-89 

wefis  of 88 

Stanislaus  Oil  Co.,  well  of 112 

Stockholders  area.  See  Standard-Stockhold- 
ers, etc.,  area. 

Stockton  Ofi  Co.,  well  of. 113 

Stratigraphy,  description  of 20-61 

See  also  particular  formations. 

Structure,  description  of 62-68,76-77,102-104 

Structure  contours,  use  of. 74-75 

Sulphur  Spring  Canyon,  definition  of 16 


S.  W.  & B.  area.  See  Mercantile  Crude-S.  W. 
& B.  area. 


T. 


Tamiosoma  zone,  character  and  distribution 

of. 36 

T.  C.  area.  See  Peerless,  etc.,  area. 

Tejon  formation,  character  and  distribution 

,of 23-27, 

76-77,  81,  82,  84,  86,  90,  99, 
100, 106,108, 109-110, 121-122 

oil  and,  relations  of 28-29,73,114 

shale  of,  age  and  relations  of 27-28 

Tejon  zone,  occurrence  and  character  of. 69 

Temblor  Range,  definition  of 13 


142 


INDEX, 


Page. 

Tent  Hills,  definition  of 14 

Tertiary  rocks,  character  and  distribution  of.  23-61 

overlaps  of. 63-64 

Topography,  description  of 16-19 

Transportation,  facilities  for 7,12,125-126 

Tulare  Lake,  description  of 19 

U. 

Unconformities,  presence  and  character  of....  63-64 
Union  area.  See  Associated,  etc.,  area. 

V. 

Vaqueros  sandstone,  character  and  distribu- 
tion of. . 29-35, 79, 90, 99, 100, 101, 106, 108 


oil  and,  relations  of 31, 35, 69-70 

sections  of 35 

Vaqueros  zones,  occurrence  and  character  of.  69-70 

W. 

Waltham  Creek,  definition  of 15 

description  of 19 

rocks  near 41-45 

Waltham  Creek -San  Joaquin  Valley  coal 

mine  area,  geology  of 99-102 

location  of 99 

section  of . 101, 104 

structure  of 102-104 

wells  of 104-106 


Page. 

Waltham  Valley,  definition  of 15 

rocks  in 37-38 

Water,  underground,  difficulty  with 11,82, 

relation  of,  to  oil 

Wells,  depth  of 7 

list  of.: 127-135 

Westside  field,  future  development  in 117-118 


See  also  Call-Confidence  area;  Mercantile 
Crude’- S.  W.  & B.  area;  Zier- 
Porter  & Scriber-M.  K.  & T. 
area;  Associated-Caiedonian-Un- 
ion  area;  Waltham  Creek- San 
Joaquin  Valley  area;  Sec.  2,  T. 
21  S.,  R.  14  E.  and  vicinity  area. 


White  Creek  basin,  rocks  in 49-50,62 

structure  of 65-66 

Z. 

Zapato  Canyon,  definition  of 16 

rocks  at 39,42-43 

section  on 51 

Zenith  Oil  Co.,  well  of 78 

Zier-Porter  & Scriber-M.  K.  & T.  area,  loca- 
tion of 93 

production  of 95 

wells  of 93-95 

log  of 95 

Zones,  oil.  See  Oil  zones. 


o 


to  oo 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  Director 


Buxletin  358 


GEOLOGY 

OF  THE 

SEWARD  PENINSULA 
TIN  DEPOSITS 

ALASKA 

By  ADOLPH  KNOPF 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1908 


CONTENTS. 


Preface,  by  Alfred  H.  Brooks : 

Introduction 

Production  and  prospecting 

Geography  of  the  region 

General  geology 

Outline 

Slates  near  York 

Port  Clarence  limestone 

Limestone  near  Palazruk 

Surficial  deposits 

Igneous  rocks 

Mineralogy  of  the  region 

Economic  geology 

Outline 

Lodes 

Ear  Mountain 

Introduction 

General  geology 

Granite 

Contact  metamorphism 

Quartz-augite  porphyry  dikes 

Mineral  occurrences 

Buck  Creek 

Geologic  features 

• Economic  geology _ 

Origin  of  the  ores 

Cape  Mountain __ 

General  geology 

Granite 

Contact  phenomena 1 

Ore  deposits - 

Developments , 

Brooks  Mountain 

Lost  River 

Location 

General  geology 

The  rocks 

Orbicular  contact  metamorphism 

Cassiterite  prospects 

Lodes 

Developments 

Seaming  of  the  limestone 

Cassiterite  and  wolframite  quartz  veins. 

Metasomatic  processes 

Wolframite-topaz  lode 


Page. 

5 

7 

8 
9 

10 

10 

10 

12 

13 

15 

15 

10 

24 

24 


20 

26 

28 

29 

30 
32 

32 

33 

34 

35 
35 

35 

36 
38 

40 

41 
44 
44 
44 

44 

45 
49 
49 
52 
52 

55 

56 

57 


3 


4 


CONTENTS. 


Economic  geology — Continued.  ' page> 

Lodes — Continued. 

Lost  River — Continued. 

Other  mineral  deposits 58 

Alaska  Chief  property 58 

Idaho  claim 59 

Origin  of  the  ores . 60 

Placers 61 

Buck  Creek 61 

Grouse  Creek 62 

Fairhaven  district 68  • 

Resume  and  conclusions 63 

Practical  deductions 66 

Index 69 


ILLUSTRATIONS. 


Plate  I.  Topographic  map  of  tin  region,  showing  location  of  metallifer- 
ous prospects 

II.  A,  Thin  section  of  paigeite  hornfels;  B,  Port  Clarence  limestone 
near  head  of  Cassiterite  Creek 

III.  A,  Thin  section  of  actinolite-cassiterite  rock;  B,  Thin  section  of 

stanniferous  metamorphosed  limestone,  from  Brooks  Moun- 
tain  

IV.  A,  Orbule  produced  by  contact  metamorphism;  B,  Reverse  side 

of  orbule  shown  in  A;  C,  Maximum  orbule;  D,  Irregular 

orbules— 

V.  Banded  vein,  supply  duct  for  orbules 

VI.  A,  Banded  apophysis  from  garnet-vesuvianite  mass  on  Tin  Creek ; 

B,  Orbules  in  marble  matrix,  showing  mode  of  origin 

VTI.  A,  Reticulate  seaming  of  limestone  in  vicinity  of  Cassiterite  lode ; 
B,  Surface  exposure  showing  occurrence  of  fluorite  silicate 

rock  adjoining  veinlets  in  limestone 

VIII.  A,  Polished  surface  of  seamed  limestone,  showing  intense  meta- 
somatism ; B,  Thin  section  of  cassiterite  ore 

IX.  A,  Polished  surface  of  wall  rock  adjoining  wolframite-quartz 
vein ; B,  Thin  section  of  wall  rock  adjoining  wolframite-quartz 

vein ^ 

Fig.  1.  Geologic  sketch  map  of  the  Seward  Peninsula  tin  region 

2.  Geologic  sketch  map  of  Ear  Mountain , 

3.  Geologic  section  through  Ear  Mountain : 

4.  Diagrammatic  section  at  Eunson’s  shaft,  Ear  Mountain 

5.  Geologic  sketch  map  of  Cape  Mountain 

6.  Geologic  section  across  Lagoon  Creek,  Cape  Mountain 

7.  Geologic  sketch  map  of  Cassiterite  Creek  and  viciuity 


Page. 


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12 


34 


44 

46 

46 


50 

54 


56 

11 

27 

27 

30 

36 

37 
45 


PREFACE. 


By  Alfred  H.  Brooks. 


Since  the  discovery  of  stream  tin  in  the  York  region  by  the  Geo- 
logical Survey  in  1900  the  tin  deposits  of  this  district  have  been  dis- 
cussed in  several  Survey  publications.  In  all  cases,  however,  the 
statements  were  based  on  investigations  that  were  incidental  to  other 
work,  and  as  this  district  had  attracted  much  notice  as  a possible 
source  of  tin  and  considerable  money  had  been  spent  in  mining  and 
prospecting,  it  appeared  time,  in  the  spring  of  1907,  to  undertake  a 
more  thorough  investigation. 

To  this  task  Mr.  Knopf  was  assigned,  with  instructions  to  make  a 
careful  study  of  the  mineral  deposits  and,  so  far  as  time  permitted, 
to  determine  the  laws  of  their  occurrence  and  origin.  It  was 
thought  best  to  emphasize  the  more  purely  scientific  phase  of  the 
investigation,  for  the  commercial  phase  can  best  be  solved  by  the 
mining  expert  and  engineer.  Therefore,  those  who  expect  to  find 
in  this  volume  a statement  of  the  commercial  value  of  individual  ore 
bodies  will  be  disappointed.  * In  the  opinion  of  the  writer,  however, 
the  presentation  of  the  chief  facts  regarding  the  mineralogy  and 
geology  of  the  tin  deposits,  together  with  a careful  analysis  of  these 
data,  will  have  more  value  to  the  district  as  a whole  than  any  at- 
tempt to  publish  a statement  of  commercial  features  of  individual 
ore  bodies.  Moreover,  it  has  become  an  established  policy  in  the 
Alaskan  work  not  to  attempt  to  sample  ore  bodies,  as  such  Avork  is 
believed  to  fall  outside  of  the  province  of  the  Federal  geologist,  and 
obviously  without  careful  sampling  the  valuation  of  any  given  de- 
posit is  impossible. 

The  reader  should  not  infer  from  the  foregoing  remarks  that  this 
paper  is  regarded  as  a final  statement  on  the  occurrence  and  genesis 
of  the  tin  deposits.  Difficulty  of  access,  limited  exposures,  and  lack 
of  time  prevented  Mr.  Knopf  from  making  exhaustive  studies.  It 
is  believed,  however,  that  this  report  marks  a great  advance  in  the 
knowledge  of  the  subject. 


5 


GEOLOGY  OF  THE  SEWARD  PENINSULA  TIN 
DEPOSITS,  ALASKA." 


By  Adolph  Knopf. 


INTRODUCTION. 

Stream  tin  was  discovered  in  the  York  region  of  Seward  Peninsula 
during  the  fall  of  1900  as  a heavy  and  objectionable  constituent  which 
accumulated  in  the  sluice  boxes  of  the  placer-gold  prospectors.  Some 
of  this  material  wTas  brought  to  Washington  by  A.  H.  Brooks,  of  the 
United  States  Geological  Survey,  who  was  engaged  in  a hasty  recon- 
naissance of  the  mineral  resources  of  the  region,  and  was  identified 
as  cassiterite.*'  The  discovery  was  soon  heralded  by  the  public  press. 

The  true  nature  and  value  of  the  mineral  once  known,  search  wras 
directed  toward  finding  a wider  distribution  of  the  stanniferous 
gravels  and  toward  locating  the  bed-rock  source  of  the  cassiterite. 
Two  factors  combined  to  stimulate  this  search — the  failure  of  the  gold 
placers  of  the  region  and  the  high  market  price  of  metallic  tin  in 
recent  years.  Ever  since  their  discovery  the  Alaskan  tin  deposits,  as 
they  are  popularly  styled,  have  continued  to  attract  considerable 
attention  from  the  mining  public — an  interest  due  in  large  part  to 
the  fact  that  there  are  no  producing  tin  mines  in  the  United  States 
proper. 

Several  reports  of  a preliminary  character  have  been  issued  by 
the  Geological  Survey  describing  the  geology  and  mineral  resources 
of  the  York  region,  in  which  the  chief  deposits  of  tin  occur.  The 
presence  of  placer  tin  in  Anikovik  River  and  in  its  tributary,  Buhner 
Creek,  was  first  recorded  by  Brooks.0  On  the  basis  of  a reconnais- 
sance of  the  northwestern  part  of  Seward  Peninsula  in  1901,  Collier  d 
was  able  to  offer' certain  advice  as  to  where  search  for  lode  tin  might 
profitably  be  made.  In  1903  he  assisted  a number  of  prospectors  in 
making  the  original  discovery  of  lode  tin  in  Seward  Peninsula  and 

° A summary  of  the  results  given  in  this  paper  was  published  several  months  ago  by 
Brooks,  A.  H.,  and  others,  in  Mineral  resources  of  Alaska  ; report  on  progress  of  investi- 
gations in  1907  : Bull.  U.  S.  Geol.  Survey  No.  345,  1908,  pp.  251-267. 

b Brooks,  A.  H.,  A new  occurrence  of  cassiterite  in  Alaska : Science,  new  ser.,  vol.  13, 
No.  328,  1901,  p.  593. 

c Brooks,  A.  H.,  An  occurrence  of  stream  tin  in  the  York  region,  Alaska : Mineral 
resources  U.  S.  for  1900,  U.  S.  Geol.  Survey,  1901,  p.  270.  Also,  A reconnaissance  of 
the  Cape  Nome  and  adjacent  gold  fields  of  Seward  Peninsula,  Alaska,  in  1900  (a  special 
publication  of  the  U.  S.  Geol.  Survey),  1901,  pp.  132-139. 

d Collier,  A.  J.,  Prof.  Paper  U.  S.  Geol.  Survey  No.  2,  1902,  p.  49. 


7 


8 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


Avas  able  to  publish  the  first  authentic  information  on  the  occurrence 
of  cassiterite  in  place.®  On  returning  from  his  examination  of  the 
Cape  Lisburne  coal  fields  in  1904,  he  spent  a few  days  in  the  York 
region  and  noted  the  progress  of  development  in  opening  up  the  tin 
deposits.6  Later  developments,  in  the  fall  of  1905,  were  fully  de- 
scribed by  Hess.® 

No  member  of  the  Survey  visited  the  region  in  1906,  but  numerous 
popular  reports  indicated  that  extensive  development  work  was  in 
progress.  Owing  to  the  fact  that  the  earlier  investigations,  which 
were  incidental  to  field  work  in  other  parts  of  Seward  Peninsula, 
were  hampered  by  lack  of  time  and  by  the  inadequate  development 
of  the  region,  it  was  deemed  advisable  to  give  an  entire  field  season 
to  an  examination  of  the  tin  deposits,  including  those  of  Ear  Moun- 
tain, which  had  not  been  preAuously  visited.  With  this  purpose  in 
view,  the  writer  was  instructed  to  examine  all  knoAvn  occurrences  of 
tin  ore  in  Seward  Peninsula,  giving  especial  attention  to  the  origin 
of  the  ores  and  the  commercial  importance  of  the  field.  Field  Avork 
Avas  commenced  at  Tin  City  on  June  23,  and  ended  at  Teller  on  Sep- 
tember 6,  1907. 

Acknowledgments  are  due  for  the  many  courtesies  extended  to  the 
writer  while  in  the  region,  and  it  is  an  especial  pleasure  to  thank  Mr. 
John  Yatney,  of  Ear  Mountain,  Mr.  M.  R.  Luther,  of  Tin  City,  and 
Messrs.  William  C.  Randt  and  S.  Read,  of  Lost  RWer,  for  their  gener- 
ous hospitality  and  substantial  aid  in  furthering  the  field  work.  Thanks 
are  also  due  Dr.  W.  T.  Schaller,  Dr.  E.  C.  Sullivan,  and  Prof.  E.  F. 
Smith  for  assistance  in  chemical  and  mineralogical  work. 


PRODUCTION  AND  PROSPECTING. 

The  total  production  of  tin  ore  in  the  entire  region  to  the  close  of 
1907  was  about  160  tons  of  concentrates,  all  of  which,  except  a few 
tons  from  lode  deposits,  came  from  the  stream  tin  of  Buck  Creek. 

The  approximate  annual  value  of  the  tin  production  of  the  York 
district  since  mining  began  is  as  follows : 


Value  of  tin  produced  in  York  region , Alaska,  1902-1907. 


1902 

1903 

1904 

1905 

1906 
.1907 


$8,  000 
14,  000 
8,  000 
4,000 
38,  640 
20.  000 


92,  640 


° Collier,  A.  J.,  Tin  deposits  of  the  York  region,  Alaska  : Bull.  U.  S.  Geol.  Survey  No.  225, 
1904.  See  also  Bull.  229. 

b Collier,  A.  J.,  Recent  development  of  Alaska  tin  deposits  : Bull.  U.  S.  Geol.  Survey 
No.  259,  1905,  pp.  120-127. 

c Hess,  F.  L .,  The  York  tin  region  : Bull.  U.  S.  Geol.  Survey  No.  284,  1906,  pp.  145-157. 


TOPOGRAPHIC  RECONNAISSANCE  MAP  OF  THE  YORK  TIN  REGION,  SEWARD  PENINSULA,  ALASKA 


GEOGRAPHY  OF  THE  REGION. 


9 


At  present  four  localities  are  being  prospected  for  tin.  They 
are  included  in  an  area  of  400  square  miles,  about  100  miles  northwest 
of  the  city  of  Nome,  the  supply  point  of  the  region.  In  geographic 
order  from  north  to  south  these  four  localities  are  Ear  Mountain, 
Buck  Creek,  Cape  Mountain,  and  Lost  River.  Ear  Mountain  occupies 
an  isolated  position  40  miles  north  of  the  others,  which  are  grouped 
together  in  the  York  region  at  the  west  end  of  the  continent. 

GEOGRAPHY  OF  THE  REGION. 

The  region  here  to  be  considered  comprises  the  extreme  western 
projection  of  Seward  Peninsula,  or  that  portion  of  the  American  Con- 
tinent which  approaches  nearest  to  Asia.  On  the  northwest  it  is 
bounded  by  the  Arctic  Ocean,  and  on  the  southwest  by  Bering  Sea — 
two  bodies  of  water  that  are  frozen  over  during  seven  months  of  the 
year.  In  1907  navigation  opened  to  Tin  City,  which  is  situated  at  the 
tip  of  the  continent,  on  June  22,  and  a few  days  later  the  last  of  the 
ice  had  drifted  northward  through  Bering  Strait.  During  the  open 
season  gasoline  schooners  maintain  a weekly  service  between  Nome 
and  points  on  Bering  Sea,  and  a small  passenger  steamer,  carrying  the 
mail,  calls  ever}^  ten  days  while  en  route  to  Kotzebue  Sound.  A 
nominal  ten-day  mail  service  is  thus  afforded  during  the  summer 
months,  but  a regular  weekly  service  is  obtained  in  the  winter  with 
sled  and  dog  team. 

The  topographic  character  of  the  region  is  well  brought  out  on  the 
map  (PI.  I).  Toward  the  north  the  Arctic  coastal  plain  forms  a 
wide  expanse  of  gently  rolling  topography  with  a relief  of  less  than 
50  feet,  and  so  heavily  grown  over  with  moss  as  to  be  practically  im- 
passable to  wagons.  Numerous  lakes  dot  the  landscape,  and  the 
streams  wind  across  the  plain  in  tortuous  courses,  emptying  into 
broad  lagoons  impounded  behind  barrier  beaches.  In  the  vicinity  of 
Shishmaref  Inlet  the  lower  stretches  of  the  streams  are  affected  b}^  the 
tidal  ebb  and  flow. 

Toward  the  south  the  York  Mountains  rise  abruptly  from  the 
coastal  plain.  They  are  an  exceedingly  steep  and  rugged  group,  with 
an  average  altitude  of  2,500  feet.  Broad  stream  valleys,  however, 
penetrate  the  mountains  from  both  the  Bering  and  Arctic  sides  and 
render  them  easily  accessible,  so  that  wagons  have  been  taken  across 
them  at  a number,  of  points  without  difficulty.  Where  the  mountains 
abut  upon  the  Bering  coast  they  are  broken  off  by  bold  sea  cliffs,  and 
a magnificent  terrace  1 to  4 miles  wide  with  gentle  seaward  slope  has 
been  carved  upon  their  flanks  at  an  elevation  of  600  to  800  feet.® 
Westward  this  feature  merges  into  the  York  Plateau — a level  upland 
surface  ranging  in  altitude  from  200  to  600  feet.  The  larger  streams 

° Collier,  A.  J.,  A reconnaissance  of  the  northwestern  portion  of  Seward  Peninsula, 
Alaska  : Prof.  Paper  U.  S.  Geol.  Survey  No.  2,  1902,  p.  37. 


10 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


have  cut  wide,  shallow  valleys  in  this  plateau,  and  these  furnish  good 
wagon  roadways  of  easy  grade. 

The  western  extremity  of  the  continent  is  marked  by  an  isolated 
mountain  mass,  known  as  Cape  Mountain,  which  rises  sheer  from  the 
water’s  edge  to  a height  of  2,250  feet.  This  impressive  promontory, 
usually  swathed  in  chill  fogs,  forms  the  American  portal  of  Bering 
Strait. 

There  are  no  harbors  in  the  region  and  consequently  landing  is 
often  impossible  on  account  of  fog,  surf,  or  storm.  The  nearest  har- 
bor is  that  of  Port  Clarence,  20  miles  distant. 

GENERAL  GEOLOGY. 

OUTLINE. 

The  sedimentary  rocks  of  the  tin  region  comprise  chiefly  limestones 
and  slates,  all  probably  of  Paleozoic  age.  The  oldest  rocks  are  a 
series  of  impure  arenaceous  slates  of  undetermined  age.  These  are 
overlain  conformably  by  a thick  formation  of  thin-bedded  Ordovician 
limestones  (Port  Clarence  limestone),  which  generally  show  no  evi- 
dence of  metamorphism.  Near  Cape  Prince  of  Wales  there  is  de- 
veloped a series  of  crystalline  limestones  with  subordinate  siliceous 
schists  and  quartzites.  These  rocks  are  of  “ Lower  Carboniferous  ” 
age,  and  are  faulted  off  against  the  slates  to  the  east.  Greenstones 
are  common  in  the  slates  and  a number  of  granite  stocks  have  invaded 
the  limestones. 

The  youngest  sediments  of  the  region  are  the  gravels,  sands,  and 
silts  of  the  Arctic  coastal  plain.  The  distribution  of  the  rocks  is  indi- 
cated on  the  sketch  map  (fig.  1),  in  which  use  has  been  made  of  the 
earlier  published  results.  In  the  succeeding  pages  the  salient  features 
of  the  various  formations  of  the  York  region  are  briefly  described,  but 
no  attempt  is  made  to  discuss  the  metamorphic  rocks  of  Ear  Mountain 
under  the  heading  of  general  geology,  inasmuch  as  their  stratigraphic 
relations  are  unknown. 

SLATES  NEAR  YORK. 

In  the  vicinity  of  York  a belt  of  slates  8 or  10  miles  wide  trends 
northwestward  across  the  west  end  of  Seward  Peninsula.  The  slates 
are  prevailingly  of  an  impure  arenaceous  character  and  exhibit  a 
variable  degree  of  metamorphism  throughout  the  area,  though  the 
great  bulk  of  the  series  consists  of  but  slightly  metamorphosed  rocks. 
Typical  black  clay  slates  are  locally  interstratified  as  thin  beds  with 
the  more  siliceous  types.  The  arenaceous  slates  are  as  a rule  more 
or  less  calcareous  or  dolomitic.  Massive  members  of  the  series  con- 
sist of  fine-grained  dolomitic  sandstone.  A graphitic  siliceous  schist 
(the  graphite,  however,  is  poorly  individualized)  represents  the 


GENERAL  GEOLOGY. 


11 


highest  phase  of  metamorphism  in  the  York  region,  but  this  type  has 
no  great  areal  distribution.  Petrographically  the  slates  consist  chiefly 
of  comminuted  quartz  and  feldspar,  and  as  an  accessory  mineral  a 
constant  though  minute  amount  of  clastic  brown  tourmaline  was 
noted  from  all  parts  of  the  area.  In  the  dolomitic  member  the  quartz 
grains  are  generally  well  rounded,  and.  the  carbonate,  whose  mag- 


Fig.  1.  Geologic  sketch  map  of  the  Seward  Peninsula  tin  region. 

nesian  character  was  determined  chemically,  is  commonly  in  the  form 
of  small  rhombohedra  scattered  throughout  the  binding  material. 

The  degree  of  cleavage  of  the  slates  is  variable.  The  rocks  range 
from  nearly  massive— rocks  little  more  than  shales— to  thinly  fissile 
slates.  Cleavage  and  stratification  may  coincide  locally,  but  within 
a short  distance  may  stand  at  right  angles.  Measurements  of  strike 


12 


TTN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


and  dip  of  the  cleavage  have  little  value  on  account  of  this  abrupt 
variation,  as  the  sedimentary  banding  can  rarely  be  observed.  These 
relations  are  best  displayed  in  the  beach  section  between  York  and 
Kanauguk  Point.  The  slates  are  affected  by  faults,  and  one  was 
noted  to  have  offset  a dike  400  feet.  They  are  fractured  and  veined 
with  quartz  stringers,  some  of  which  carry  cassiterite,  blue  tourma- 
line, arsenopyrite,  and  pyrite. 

The  slates  are  faulted  against  a series  of  crystalline  limestones  on  the 
west,  and  underlie  the  Port  Clarence  limestone  conformably  on  the  east. 

PORT  CLARENCE  LIMESTONE. 

The  Port  Clarence  limestone  was  so  named  by  Collier  a on  account 
of  its  typical  exposure  north  of  Port  Clarence,  where  it  occupies  an 
area  of  1,400  square  miles.  Mere  it  comprises  a thick  volume  of  thin- 
bedded  limestones  of  dense  texture,  generally  unaffected  by  metamor- 
phism. Four  types  of  rock  can  be  discriminated — an  ash-gray  vari- 
ety, a dark  lead-gray  variety,  magnesian  and  tremolitic  phases,  and 
an  argillaceous  banded  variety.  The  first  two  are  the  commonest 
types,  and  occur  together  in  interstratified  beds.  The  dark  lead -gray 
limestone  forms  massive  beds  up  to  G feet  thick,  but  the  ash-gray 
variety,  which  is  fine  grained,  like  lithographic  stone,  is  thin  bedded 
and  commonly  breaks  into  large,  thin  slabs  whose  surfaces  are  covered 
with  fucoid  fragments.  These  limestones  were  found  to  be  nonmag- 
nesian  in  the  specimens  examined,  the  ash-gray  variety  containing 
considerable  aluminous  material,  and  the  dark  lead-gray  limestone 
being  pure  carbonate  rock.  Some  beds  of  fine-grained  dolomite  occur 
in  the  Port  Clarence  formation,  but  on  account  of  their  close  resem- 
blance to  the  prevailing  dense-textured  limestones  their  quantitative 
abundance  is  not  known.  Occasionally  there  occur  interbedded  with 
the  normal  Port  Clarence  limestones  strata  which  show  numerous 
small  prisms  of  tremolite  in  random  orientation.  This  is  the  highest 
degree  of  metamorphism  displayed  by  the  formation,  except  for 
purely  local  manifestations  surrounding  granitic  intrusives. 

The  basal  portion  and  lower  horizons  of  the  Port  Clarence  forma- 
tion consist  of  an  impure  banded  limestone,  the  banding  being 
produced  by  laminae  of  argillaceous  material.  This  phase  is  com- 
monly in  a highly  contorted  condition  (PL  II,  B).  Locally,  as  at 
Cassiterite  Creek,  tremolite  has  been  noted  as  an  abundant  constit- 
uent, though  the  possibility  is  not  excluded  that  the  amphibole 
may  have  been  produced  by  the  action  of  vein- forming  agencies. 

In  the  Lost  Kiver  region  the  Port  Clarence  has  a thickness  of 
2,000  feet.  Collier  6 has  indicated  that  the  thickness  may  be  as  great 

a Collier,  A.  J.,  Reconnaissance  of  the  northwestern  portion  of  Seward  Peninsula, 
Alaska  : Prof.  Paper  IT.  S.  Geol.  Survey  No.  2,  1002,  p.  18. 

b Collier,  A.  J.,  Tin  deposits  of  the  York  region,  Alaska  : Bull.  U.  S.  Geol.  Survey  No.  229, 
1904,  p.  19. 


U.  S.  GEOLOGICAL  SURVEY  BULLETIN  NO.  358  PL.  II 


A.  THIN  SECTION  OF  PAIGEITE  HORNFELS. 

Magnification  60  diameters.  Black,  opaque  fibers  of  paigeite  in  tourmaline.  Colorless  mineral  is  fluorite. 


B.  PORT  CLARENCE  LIMESTONE  NEAR  HEAD  OF  CASSITERITE  CREEK. 
Showing  crumpled  character  of  the  argillaceous  banded  variety. 


GENERAL  GEOLOGY. 


13 


as  5,000  feet,  but  on  account  of  the  prevalence  of  faults  and  shatter 
zones  in  this  region  it  is  probable  that  the  smaller  figure  is  more 
nearly  correct.  The  dip  of  the  limestone  is  usually  low — about 
20°  N. — although  it  may  reach  as  high  as  60°  along  the  upper  course 
of  Kanauguk  River. 

The  Port  Clarence  limestone  overlies  the  slates  of  the  York  region 
conformably.  As  exposed  along  the  western  flank  of  the  York 
Mountains  the  basal  argillaceous  schistose  limestones  of  the  Port 
Clarence  formation  merge  imperceptibly  into  members  of  the  slates, 
the  transitional  zone  being  several  hundred  feet  thick.  The  same 
relations  are  evident  on  the  northwest  flank  of  Brooks  Mountain, 
where  the  transition  is  more  abrupt,  but  is  marked  by  an  intimate 
interlamination  of  slate  and  limestone.  The  transition  zone  has 
been  a zone  of  weakness,  and  exhibits  more  or  less  severe  dynamic 
deformation.  As  already  indicated,  the  lower  horizons  of  the  Port 
Clarence  are  acutely  crumpled,  locally  passing  into  a brecciated 
condition.  Viewed  in  the  large,  however,  this  phase  maintains  the 
appearance  of  undisturbed  and  simple  structure,  characteristic  of 
the  Port  Clarence  as  a whole. 

Farther  east,  in  the  vicinity  of  Bay  Creek,  the  Port  Clarence 
limestone  gives  place  to  the  graphitic,  chloritic,  and  calcareous 
schists  characteristic  of  the  Xome  region.  The  exact  relations  are, 
however,  obscure.  In  the  hills  behind  Teller  Mission  the  limestone  is 
highly  argillaceous  and  in  many  places  acutely  contorted,  indicating 
that  the  basal  portion  of  the  Port  Clarence  is  exposed.  According  to 
this  interpretation  the  Port  Clarence  is  regarded  as  folded  into  a 
synclinorium,  with  one  limb  exposed  on  the  western  flank  of  the  York 
Mountains  and  the  other  at  Bay  Creek.  Subordinate  folds  have 
brought  the  underlying  slates  into  the  zone  of  erosion  in  isolated 
areas,  as  at  Brooks  Mountain  and  California  River. 

The  age  of  the  Port  Clarence  limestone,  according  to  Collier,®  is 
either  Ordovician  or  Silurian.  The  writer  found  at  the  head  of 
’ Cassiterite  Creek  a few  poorly  preserved  fossils,  which,  as  identi- 
fied by  Kindle,  appear  to  belong  to  the  genera  RapJiistoma  and 
Liospira , indicating  an  Ordovician  age. 

LIMESTONE  NEAR  PALAZRUK. 

Between  the  granite  headland  of  Cape  Prince  of  Wales  and  the 
mouth  of  Baituk  Creek  is  a belt  of  crystalline  limestone,  which  is 
finely  exposed  in  the  cliffs  that  front  Bering  Sea.  Sericitic  siliceous 
schists,  phyllites,  and  thin-bedded  white  quartzite  are  present,  but  are 
of  very  subordinate  importance.  . The  siliceous  schists  find  their  main 

B Collier,  A.  J.,  The  gold  placers  of  a part  of  Seward  Peninsula : Bull.  U.  S.  Geol.  Survey 
No.  328,  p.  79. 


14 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


development  on  Cape  Mountain,  where  they  are  apparently  300  feet 
thick,  and  overlie  the  limestone  capping  the  summit  of  the  granite 
stock. 

A striking  feature  of  the  limestone  is  the  variable  degree  of  meta- 
morphism which  it  exhibits  in  different  parts  of  the  area.  It  varies 
from  a dense-textured  dark-blue  limestone  oh  the  north  side  of  Cape 
Mountain  to  a faintly  schistose  snow-white  marble  in  the  section  dis- 
played along  Bering  Sea. 

The  thermal  metamorphism  produced  by  the  granite  invasion  is 
strictly  local  in  character.  Marmorization  extends  200  feet  from  the 
intrusive  at  a maximum,  producing  a coarsely  granular  aggregate  of 
calcite  crystals  several  millimeters  in  diameter.  The  calcareous 
quartzites,  however,  remain  unaffected  at  this  distance.  In  the  lime- 
stone patch  overlying  the  granite  the  siliceous  laminae  have  been  con- 
verted into  wollastonite  bands  which  exhibit  a remarkable  degree  of 
minute  crinkling.  Some  phases  of  the  limestone  show  a development 
of  metamorphic  minerals  unconnected  with  the  presence  of  visible 
intrusives.  In  the  old  sea  cliff  1 mile  east  of  Tin  City  a series  of  in- 
terstratified  ash-gray  and  dark-blue  beds,  each  individually  a few  feet 
or  less  in  thickness,  show  numerous  foils  of  phlogopite,  long  prisms 
and  radial  groups  of  tremolite,  and  cubes  of  pyrite.  Phlogopite  is 
areally  the  most  persistent  mineral,  and  the  phlogopite-bearing  lime- 
stone can  be  traced  as  far  west  as  the  head  of  Cape  Creek.  A cer- 
tain original  content  of  magnesia  is  indicated  by  the  formation  of 
phlogopite  and  tremolite  and  can  be  detected  chemically  in  the  car- 
bonate of  the  dark-blue  limestone.  Whether  the  formation  of  these 
minerals  is  due  to  thermal  metamorphism  is  an  open  question,  but 
the  field  evidence  suggests  that  it  has  been  caused  by  the  same  agency 
which  produced  the  crystalline  marbles — namely,  a mild  regional 
metamorphism. 

The  structure  within  the  limestone  area  is  prevailingly  simple. 
The  beds  lie  nearly  horizontal,  with  a slight  easterly  dip.  Here  and 
there  rolls  with  dips  up  to  20°  occur.  Locally  individual  strata  are 
acutely  crumpled  and  doubled  back  upon  themselves.  On  the  basis 
of  relative  degree  of  metamorphism  this  limestone  would  be  regarded 
as  the  oldest  formation  in  the  York  region,  but  paleontologic  evi- 
dence procured  by  Collier®  has  shown  it  to  be  of  Mississippian 
(“  Lower  Carboniferous  ”)  age — younger  than  the  less  highly  meta- 
morphosed Port  Clarence  limestone  8 miles  east  of  it.  The  limestone 
appears  to  be  faulted  against  the  slates  on  the  east.  Both  formations 
are  lying  flat  near  the  contact,  though  locally  the  limestone  may  show 
almost  vertical  dips.  The  line  of  contact,  however,  does  not  follow 
the  contours  as  it  should  if  one  horizontal  formation  were  resting 

* Collier.  A.  J.,  The  gold  placers  of  a part  of  Seward  Feninsula : Bull.  U.  S.  Geol. 
Survey  No.  328,  p.  81. 


GENERAL  GEOLOGY. 


15 


upon  the  other,  but  cuts  across  them  indifferently.  Furthermore,  va- 
rious friction  breccias  are  found  in  the  vicinity  of  the  contact,  and  an 
abundant  quartz  veination  occurs  in  the  slates.  These  features — the 
shattering,  crushing,  and  local  dragging  of  the  strata,  and  the  fact 
that  the  contact  is  independent  of  the  topography — indicate  that  the 
limestone  is  cut  off  to  the  east  by  a fault. 

SURFICIAL  DEPOSITS. 

Surficial  deposits  have  a relatively  small  distribution  in  the  York 
region.  They  comprise  the  shallow  gravels  of  the  present  streams 
and  the  beach  deposits  of  the  narrow  coastal  shelf  bordering  Bering 
Sea.  Toward  the  north,  however,  all  bed  rock  is  mantled  by  the 
silts  and  gravels  beneath  the  low-rolling  arctic  tundra  that  stretches 
between  Cape  Prince  of  Wales  and  Cape  Espenberg.® 

Some  of  the  stream  gravels  contain  local  concentrations  of  gold 
and  placer’ tin,  and  are  therefore  of  economic  interest. 

IGNEOUS  ROCKS. 

Four  stocks  of  granite  are  intrusive  into  the  limestones  of  the 
region,  all  quartzose  orthoclase  granites  containing  subordinate 
amounts  of  sodic  oligoclase  and  biotite,  and  all  prevailingly  of  a 
coarsely  granular  porphyritic  habit.  They  appear  to  represent  con- 
temporaneous intrusions;  and  as  the  granite  at  Cape  Prince  of  Wales 
is  known  to  invade  limestones  of  “Lower  Carboniferous  ” (Missis- 
sippian)  age,  it  is  probable  that  all  are  post-Mississippian.  Together 
with  related  quartz-bearing  porphyry  dikes,  they  are  the  most  im- 
portant igneous  rocks  of  the  region,  inasmuch  as  the  tin  deposits 
are  directly  associated  with  them,  and  their  description  is  therefore 
given  in  greater  detail  under  the  separate  localities  at  which  each 
occurs. 

Greenstones  of  diabasic  character  are  common  in  the  slate  area 
near  York.  Where  their  relations  can  be  determined  they  are  found 
to  be  present  as  intrusive  sills.  The  texture  of  the  greenstones  ranges 
from  aphanitic  to  coarsely  granular,  and  petrographic  examination 
shows  that  they  are  composed  essentially  of  chloritized  augite  and 
altered  plagioclase  in  ophitic  arrangement,  with  abundant  accessory 
ilmenite  and  leucoxene.  In  many  places  the  alteration  is  exceedingly 
thorough,  but  the  rPcks  are  unaffected  by  shearing. 

Narrow  basalt  dikes  of  rare  occurrence  are  found  cutting  both 
limestones  and  granite,  and  are  therefore  the  youngest  igneous  rocks 
of  the  region. 


° Collier,  A.  J.,  Prof.  Paper  U.  S.  Geol.  Survey  No.  2,  1002,  p. 


16 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


MINERALOGY  OF  THE  REGION. 

The  world’s  supply  of  tin  is  obtained  from  cassiterite,  the  dioxide 
of  tin  (78. 6 per  cent  Sn).  At  a very  few  places  stannite,  a complex 
sulphide  of  copper,  tin,  iron,  and  zinc,  has  been  found  in  sufficient 
quantities  to  be  raised  as  an  ore,  but  apparently  never  for  its  tin. 
The  stannite  formerly  found  so  abundantly  in  the  Carn  Brea  mines 
in  Cornwall  was  sold  simply  for  the  copper  it  contained.®  In  recent 
years  only  one  occurrence  is  known,  namely,  at  the  Oonah  mine  in 
Tasmania,* 6  where  an  argentiferous  stannite  has  been  mined  as  a 
copper-silver  ore.  The  tin  was  rejected  as  waste  product,  but  ar- 
rangements were  finally  made  with  the  smelter  that  for  ore  contain- 
ing at  least  8 per  cent  of  tin  $5  per  ton  should  be  paid  in  addition  to 
the  ordinary  returns  for  copper  and  silver.  The  latest  reports  from 
Tasmania  indicate,  however,  that  difficulty  has  been  experienced  in 
treating  the  stannite  ore.®  At  Borah  Creek,  New  South  Wales, d 
stannite  is  also  found,  and  occurs  associated  with  chalcopyrite,  arseno- 
pyrite,  and  galena  in  a silver-quartz  ore.  With  these  two  exceptions 
stannite  is  of  rare  occurrence  and  is  not  regarded  as  an  ore  of  tin. 

Cassiterite  is  the  only  mineral  likely  to  be  of  economic  importance 
as  a source  of  tin  in  the  Seward  Peninsula  region.  Stannite  in  as- 
sociation with  galena  and  wolframite  is  known  from  one  locality 
only,  and  there  the  prospective  value  of  the  deposit  is  probably  in 
silver  and  tungsten,  and  not  in  tin. 

Placer  gold  is  found  with  the  stream  tin  of  the  York  region,  but 
its  paragenesis  with  relation  to  the  cassiterite  is  unknown. 

The  Seward  Peninsula  tin  deposits  are  associated  with  granitic 
intrusives  which  have  invaded  various  series  of  limestones.  The 
magmas  were  rich  in  mineralizers  and  produced  an  intense  pneu- 
matolytic  contact  metamorphism  along  their  margins.  Conspicuous 
among  the  products  of  this  activity  are  the  prevalent  boron  minerals, 
tourmaline,  axinite,  a boron  vesuvianite,  ludwigite,  and  two  magne- 
sian iron-tin  borates  new  to  science,  which  have  been  named  liulsite 
and  paigeite.  Fluorite,  scapolite,  and  cliondrodite  prove  the  presence 
of  the  halogens  in  the  magmatic  exhalations,  and  sulphur  is  indicated 
by  the  various  metallic  sulphides  that  have  formed  in  the  contact- 
metamorphic  rocks. 

A total  of  52  minerals  are  listed  from  the  region,  16  of  which  have 
not  previously  been  recorded  and  two  of  which  are  new  species. 

Gold. — Some  of  the  streams  of  the  York  region  carry  placer  gold. 
In  fact,  the  prevalence  of  an  undesirable  heavy  brown  mineral  in  the 

° Trans.  Royal  Geol.  Soc.  Cornwall,  vol.  7,  p.  85. 

6 Waller,  G.  A.,  Zeehan  silver-lead  mining  field,  Govt.  Geol.  Office,  Tasmania,  1904. 

c Progress  of  the  mineral  industry  for  the  quarter  ending  30th  September,  1907, 
Govt.  Geol.  Office,  Tasmania,  p.  10. 

d Min.  Res.  New  South  Wales,  Geol.  Survey,  New  South  Wales,  p.  120. 


MINERALOGY  OF  THE  REGION. 


17 


sluice  boxes  of  the  placer-gold  miners  led  to  the  discovery  of  cas- 
siterite  and  to  the  search  for  its  bed-rock  source.  Placer  gold  is  asso- 
ciated with  the  cassiterite  of  Buck  Creek,  the  only  locality  from 
which  there  has  been  an  actual  production  of  stream  tin,  but  no 
authentic  figures  are  available  as  to  the  amount  of  gold  obtained  per 
ton  of  concentrates.  Nuggets  up  to  $20  have  been  obtained.® 

Stibnite  (Sb2S3;  71.4  per  cent  antimony). — Some  float  stibnite, 
associated  with  purple  fluorite,  was  found  in  the  saddle  at  the  head  of 
Tin  Creek  by  H.  E.  Angstadt,  of  the  Survey  party. 

Molybdenite. — Molybdenite  occurs  in  sparing  amount,  associated 
with  cassiterite,  in  the  Lost  River  region. 

Galena. — On  Brooks  Mountain,  galena,  associated  with  an  iron- 
rich  zinc  blende,  occurs  intergrown  with  minerals  of  contact-meta- 
morphic  origin.  The  Ear  Mountain  occurrences  are  of  similar  nature. 
In  the  Lost  River  region  it  occurs  in  fracture  zones  in  the  Port  Clar- 
ence limestone.  One  occurrence  in  this  region  is  absolutely  unique, 
namely,  galena  associated  with  stanniter  and  wolframite  in  a vein 
filling  of  topaz  and  fluorite. 

Sphalerite. — Sphalerite  (zinc  blende)  of  contact-metamorphic 
origin  is  common  on  Brooks  Mountain.  It  possesses  a brilliant  black 
luster  identical  with  that  of  wolframite,  with  which  mineral  it  has 
been  confused.  Analysis  by  W.  T.  Schaller  shows  that  specimens  con- 
tain 19  per  cent  of  ferrous  iron.  It  is  distinguished  from  wolframite 
by  its  inferior  gravity  (sphalerite  having  a specific  gravity  of  4 and 
wolframite  of  7.3),  greater  softness,  and  more  complex  cleavage. 
Wolframite  shows  but  a single  cleavage  direction;  sphalerite  may 
show  as  many  as  six.  Some  thin  quartz-tourmaline  veinlets  earning 
pyrite  and  lustrous  black  sphalerite  were  found  cutting  the  granite  of 
Ear  Mountain.  In  this  material  blowpipe  tests  were  necessary  to  dis- 
tinguish the  sphalerite  from  wolframite.  A small  amount  of  sphal- 
erite of  somewhat  resinous  appearance  is  found  associated  with  the 
tin  ore  on  Cassiterite  Creek. 

Pyrrhotite. — Magnetic  iron  pyrites,  or  pyrrhotite,  is  found,  together 
with  galena  and  sphalerite  of  contact-metamorphic  origin,  on  Brooks 
Mountain.  Considerable  amounts  of  it  occur  in  a copper  prospect  at 
the  mouth  of  Tin  Creek.  Small  amounts  are  disseminated  in  the 
pyroxene  hornfels  at  Cape  Mountain.  Pyrrhotite  is  commonly  re- 
garded as  stannite  throughout  the  tin  region,  but  can  infallibly  be 
distinguished  from  that  mineral  by  its  magnetic  character. 

Chalco'pyrite. — Yellow  copper  pyrites,  associated  with  pyrrhotite,  is 
found  in  a fluorite  gangue  near  the  mouth  of  Tin  Creek.  The  lime- 
silicate  hornfels  surrounding  the  granite  of  Ear  Mountain  is  locally 
flecked  with  chalcopyrite. 

a Oral  communication  by  F.  L.  Hess. 

54356— Bull.  358—08 2 


18  TIN  DEPOSITS  OE  SEWARD  PENINSULA,  ALASKA. 

Pyrite. — Irregular  disseminations  of  pyrite  occur  in  the  granite  of 
Cape  Mountain.  It  is  a common  constituent  in  the  tin  ores  of  the 
region,  and  occurs  in  the  form  of  roiled  nuggets  with  the  stream  tin 
of  Buck  Creek. 

Arsenopyrite. — The  silver-white  sulphide  of  iron  and  arsenic  occurs 
in  considerable  abundance  in  the  tin  ore  of  Cassiterite  Creek,  and  is 
found  in  the  contact-metamorphic  deposits  of  Brooks  Mountain,  as- 
sociated with  tourmaline,  fluorite,  sphalerite,  etc.  It  occurs  with 
actinolite  and  cassiterite  in  the  Buck  Creek  region. 

Stannite  (tin  pyrites;  29.5  per  cent  copper,  27.5  per  cent  tin). — 
The  rare  mineral  stannite,  a sulphide  of  copper,  tin,  iron,  and  usually 
zinc,  is  known  from  Lost  River  only,  where  it  occurs  associated  with 
galena  and  wolframite  in  a gangue  of  topaz  and  fluorite.  The  Alas- 
kan stannite  gives  a strong  qualitative  reaction  for  zinc.  It  has  a 
brown-black  color  and  a metallic  luster,  and  possesses  an  imperfect 
cleavage.  Stannite  is  a mineral  whose  identification  in  any  particular 
case  must  be  confirmed  by  chemical  examination. 

Fluorite. — Fluorite  occurs  in  a variety  of  ways  throughout  the 
region — as  a contact-metamorphic  mineral,  as  a gangue  mineral  of  tin 
and  of  copper  deposits,  and  as  a metasomatic  replacement  of  limestone 
adjoining  stanniferous  veinlets.  It  shows  a variety  of  colors — purple, 
green,  yellow,  rose — and  is  also  colorless,  but  the  purple  is  the  most 
common.  Specimens  from  the  Cassiterite  lode  show  numerous  cubes 
and,  rarely,  aggregates  of  columnar  crystals.  Fluorite  is  distin- 
guished from  quartz  by  its  relative  softness  and  fine  octahedral 
cleavage.  A characteristic  feature  is  its  power  of  phosphorescence, 
which  becomes  highly  conspicuous  during  the  drying  of  ore  samples. 

Quartz. — The  granites  of  the  region  contain  abundant  quartz,  which 
is  prevailingly  of  a smoky  character.  The  quartz  porphyry  dikes 
contain  numerous  sharply  defined  crystals  of  quartz,  and  these,  too, 
are  commonly  smoky,  and  consequently  have  been  mistaken  for  cas- 
siterite to  some  extent.  Greasy  milk-white  quartz  (“  vein  quartz  ”) 
carrying  cassiterite  forms  stringers  cutting  the  slates  of  the  York 
area. 

Hematite. — Nuggets  of  red  oxide  of  iron  occur  with  the  stream  tin 
of  Buck  Creek.  Hematite  is  used  as  a pigment  by  the  Eskimos  of 
Shishmaref  Inlet. 

Ilmenite. — Ilmenite  occurs  as  an  abundant  microscopic  constituent 
of  the  greenstones,  and  is  largely  converted  to  leucoxene. 

Spinel. — Perfect  little  octahedra  of  black  spinel  are  found  associ- 
ated with  chondrodite  in  contact-metamorphosed  limestone  near 
Read’s  galena  prospect  on  Brooks  Mountain. 

Magnetite. — Nuggets  of  magnetite  (magnetic  iron  ore)  are  fairly 
common  in  the  stream  tin  of  Buck  Creek.  The  ore  is  found  in  place 
in  visible  crystals  and  clumps  associated  with  calcite,  hulsite,  and 


MINERALOGY  OF  THE  REGION. 


19 


vesuvianite  on  Brooks  Mountain,  and  occurs  also  in  narrow  bands  in 
contact-metamorphic  limestone  at  Tin  Creek. 

Cassiterite  (Sn02;  78.6  per  cent  tin). — Cassiterite  is  a mineral 
which  can  not  be  positively  identified  by  the  eye  alone.  The  only 
convincing  test  is  the  actual  production,  from  specimens  in  question, 
of  beads  of  metallic  tin.  On  account  of  the  difficulty  of  recognizing 
cassiterite  the  prospectors  of  the  region  have  mistaken  for  it  a great 
variety  of  minerals,  including  garnet,  black  tourmaline,  augite  in 
quartz  porphyry  dikes,  pyroxene  in  contact-metamorphosed  lime- 
stone, smoky  quartz,  vesuvianite,  and  wolframite.  In  color  the 
Alaskan  cassiterite  varies  from  black  to  light  yellowish  or  almost 
colorless.  Some  from  Cape  Mountain  and  Lost  River  was  noted  to 
show  a fair  degree  of  cleavage,  which  increases  its  resemblance  to 
pyroxene.  The  specific  gravity  of  cassiterite  is  about  7 — considerably 
higher  than  that  of  the  other  minerals  mistaken  for  it,  except  wol- 
framite. Crushing  and  panning  may  therefore  serve  as  a rough  test, 
a gray  or  colorless  residue  in  the  pan  indicating  cassiterite.  But 
inasmuch  as  considerable  useless  prospecting  has  been  done  on  min- 
erals mistaken  for  cassiterite,  it  seems  advisable  to  test  the  suspected 
minerals  for  the  only  conclusive  property  of  cassiterite — its  ability 
to  yield  metallic  tin.  Pebbles  and  rolled  grains  of  cassiterite  occur- 
ring in  stream  gravels  are  known  as  stream  tin.  That  of  Buck  Creek 
is  prevailingly  of  a brown  color,  and  much  of  it  contains  small 
cavities  lined  with  clear,  glassy,  yellow  crystals.  Quartz  adheres  to 
many  of  the  larger  nuggets. 

Rutile. — Rutile  occurs  as  a microscopic  constituent  in  the  granites 
of  Cape  Mountain. 

Pyrolusite. — Perfect  dendrites,  which  are  referred  to  pyrolusite, 
occur  on  the  joint  planes  of  the  limestone  near  the  Cassiterite  lode. 

Limonite. — Limonite  occurs  very  abundantly  in  the  gossan  of 
galena  bodies  in  the  Lost  River  region. 

Calcite. — The  limestones  in  immediate  proximity  to  the  granite 
bosses  of  the  region  have  been  converted  into  aggregates  of  coarse 
white  calc  spar  in  many  places.  On  the  Dolcoath  lode,  near  Cassiter- 
ite Creek,  finely  crystallized  cassiterite  occurs  embedded  in  coarsely 
crystalline  calcite  associated  with  danburite,  tremolite,  and  topaz. 

Dolomite. — Certain  strata  of  the  Port  Clarence  limestone  are  com- 
posed of  dolomite.  It  occurs  also  in  the  form  of  minute  rliombo- 
hedra  in  some  of  the  slates  of  the  York  area. 

Cerusite. — The  gossan  of  a galena  prospect  on  Tin  Creek  was 
noted  to  contain  white  crystals  of  cerusite  (lead  carbonate). 

Azurite. — Rock  from  the  wolframite-topaz  lode  on  Lost  River  is 
slightly  incrusted  with  the  blue  copper  carbonate,  azurite,  doubtless 
derived  from  the  oxidation  of  stannite  in  the  ore. 


20  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

Feldspar. — Large  porphyritic  crystals  of  orthoclase  and  micro- 
cline  occur  in  the  granites  of  the  region.  Albite  was  detected  as  a 
constituent  of  the  wolframite-quartz  veins  on  Cassiterite  Creek. 
Plagioclase  is  common  in  the  igneous  rocks  of  the  region,  and  in  the 
limestones  as  a metasomatic  mineral. 

Pyroxene. — Large  crystals  of  augite,  up  to  2 inches  in  size,  occur  as 
a constituent  of  a quartz  porphyry  dike  on  Ear  Mountain.  They 
are  of  brown  color  and  rarely  show  cleavage  visible  to  the  eye.  They 
have  been  mistaken  for  cassiterite  and  have  occasioned  considerable 
useless  prospecting.  Augite  is  approximately  half  as  heavy  as  cas- 
siterite, and  is  readily  fusible  before  the  blowpipe.  By  this  simple 
test  with  the  blowpipe,  were  it  available  to  the  prospector,  all  the 
minerals  usually  mistaken  for  cassiterite,  except  smoky  quartz,  might 
be  rejected  from  consideration.  Pyroxene,  probably  near  heden- 
bergite  in  composition,  is  common  in  the  contact-metamorphosed 
limestone  adjoining  the  granites  of  the  region,  particularly  that  of 
Cape  Mountain.  It  resembles  some  of  the  cassiterite  very  closely, 
and  the  contact  rocks  have  been  prospected  for  tin.  This  fallacy 
is  encouraged  by  the  fact  that  the  contact  rocks  are  relatively  heavy, 
having  a weight  corresponding  to  a 10  per  cent  quartz-tin  ore. 

I V ollastonite. — Wollastonite  occurs  on  Cape  Mountain  in  proximity 
to  the  granite,  locally  forming  white  masses  up  to  3 feet  in  thickness. 

Amphibole. — Tremolite,  the  colorless  variety  of  amphibole,  is 
prevalent  in  the  form  of  glistening  white  fibers  in  the  limestone  ad- 
joining the  cassiterite  occurrences  on  Cassiterite  Creek.  It  also 
occurs  as  fine  radial  groups  in  the  limestone  east  of  Tin  City.  The 
light-green  variety,  actinolite,  constitutes  the  gangue  material  of 
some  newly  discovered  tin-bearing  rocks  on  Buck  Creek.  Horn- 
blende is  common  in  the  limestone  adjoining  cassiterite  veinlets, 
and  gives  it  a dark-green  color. 

Garnet. — As  a product  of  contact  metamorphism  garnet  is  of 
widespread  occurrence,  the  finest  specimens  coming  from  Tin  Creek, 
on  Lost  River.  It  is  commonly  crystallized  in  rhombic  dodecahedral 
forms,  yielding  diamond-shaped  faces.  Where  only  the  apex  of  the 
dodecahedron  is  visible  garnet  bears  a deceptive  resemblance  to  the 
four-sided  pyramid  characteristic  of  cassiterite.  Yesuvianite  is 
usually  associated  with  the  garnet. 

Olivine. — Olivine  forms  part  of  the  basalt  dikes  of  Cape  Mountain, 
and  is  noted  only  microscopically. 

Scapolite. — Chlorine-bearing  scapolites  are  found  in  specimens  of 
lime-silicate  hornfels  from  Ear  Mountain  and  Cape  Mountain.  Its 
identification  is  possible  only  by  microscopical  and  chemical  methods. 
In  a number  of  specimens  it  was  found  that  the  birefringence,  as 
indicated  by  the  negative  uniaxial  interference  figures,  ranged  from 
low  to  comparatively  high  values  in  the  same  thin  section. ' 


MINERALOGY  OF  THE  REGION. 


21 


Vesuvianite. — Vesuvianite  is  one  of  the  commonest  contact-meta- 
morphic  minerals  of  the  region.  It  is  especially  prevalent  on  Brooks 
Mountain  and  along  the  headwaters  portion  of  Yankee  Creek,  where 
fine  crystals  showing  ideal  development  occur  in  great  abundance 
embedded  in  a matrix  of  coarsely  crystalline  calcite.  The  color  of 
the  vesuvianite  is  some  tone  of  green,  ranging  from  gray-green  to 
brown-green.  The  crystals  are  usually  in  the  form  of  square  prisms.® 
As  radial  aggregates  and  branching  forms,  vesuvianite  associated 
with  garnet  is  abundant  near  the  granite  of  Tin  Creek  on  Lost 
River.  It  also  forms  metasomatically  near  stanniferous  veinlets  in 
limestones. 

Zircon. — Zircon  is  noted  as  a microscopic  constituent  of  the  gran- 
ites of  the  region. 

Dariburite. — The  rare  borosilicate  of  lime,  danburite,  was  identified 
as  the  gangue  material  of  cassiterite  in  the  Dolcoath  lode  on  Cas- 
siterite  Creek,  where  it  occurs  as  replacement  both  of  the  dike  rock 
and  of  the  contiguous  limestones.  (For  partial  analysis  see  p.  52.) 
The  optical  properties  of  the  danburite  in  thin  section  are  indecisive ; 
it  is  colorless  and  biaxial  and  shows  the  interference  tints  of  feldspar 
and  a relief  near  that  of  the  associated  tourmaline. 

Topaz. — As  a constituent  of  the  tin  ore  in  the  Lost  River  region 
topaz  (fluosilieate  of  aluminum)  is  exceedingly  abundant.  It  occurs 
in  altered  quartz  porphyry  dikes,  as  vein  mineral  in  veinlets  in  lime- 
stones, and  as  a metasomatic  product  in  the  limestone  adjoining  such 
veinlets.  It  is  commonly  associated  with  fluorite  and  zinnwaldite. 
The  most  remarkable  occurrence,  lioAvever,  is  that  on  the  Oregon 
claim,  where  delicatety  radial  topaz  with  subordinate  fluorite  forms 
the  gangue  of  an  argentiferous  ore  containing  wolframite,  galena, 
and  stannite.  (For  analysis  see  p.  58.) 

Zoisite. — -Zoisite  occurs  in  small  amount  in  lime-silicate  hornfels 
on  Ear  Mountain. 

Epidote. — Radial  groups  of  epidote  are  found  on  Brooks  Mountain 
near  the  granite  contact. 

Axinite. — Small  crystalline  aggregates  of  axinite  occur  in  a tour- 
maline hornfels  from  Ear  Mountain.  It  is  highly  glassy  in  appear- 
ance and  of  a peculiar  brown  color.  Many  of  the  crystal  faces  are 
striated  and  acute  edged.  Axinite  also  occurs  microscopically  in  a 
contact-metamorphi^  deposit  on  Brooks  Mountain,  associated  with 
tourmaline,  fluorite,  arsenopyrite,  and  sphalerite. 

Chondrodite. — Small  honey-yellow  crystals  of  chondrodite  occur, 
together  with  numerous  minute  black  octahedra  of  spinel,  in  a con- 
tact-metamorphosed limestone  on  Brooks  Mountain. 

Tourmaline. — Tourmaline  is  exceedingly  common  throughout  the 
entire  region  and  is  regarded  by  many  of  the  local  prospectors  as  an 

a Forms  measured  crystallographically  are  given  in  Am.  Jour.  Sci.,  4tli  ser.,  vol.  25, 
1908,  p.  323. 


22 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


infallible  indication  of  tin  ore.  Although  it  is  true  that  tourmaline 
is  pretty  generally  associated  with  cassiterite,  it  is  far  from  true  that 
cassiterite  is  always  associated  with  tourmaline.  Great  deposits  of 
tourmaline  that  carry  no  tin  whatever  are  known  in  various  parts  of 
the  world. 

In  the  Seward  Peninsula  tin  region  tourmaline  occurs  in  a great 
variety  of  ways.  It  is  found  in  granite  apophyses  on  Ear  Mountain 
as  an  original  constituent  (of  the  pneumatolytic  stage  of  consolida- 
tion). It  forms  an  essential  mineral  of  the  lime-silicate  rocks  sur- 
rounding the  granite  and  occurs  along  seams  and  stringers  in  the 
granite  itself,  and  in  the  quartz  porphyry  dikes  with  fluorite,  arseno- 
pyrite,  and  possibly  cassiterite.  On  Cape  Mountain  it  is  abundant 
in  the  granite,  and  also  occurs  embedded  in  coarsely  granular  calcite. 
In  the  Buck  Creek  area  the  quartz  stringers  contain  small  rosettes  of 
blue  tourmaline.  It  is  common  in  the  Lost  liiver  and  Brooks  Moun- 
tain regions.  Black,  dark  blue,  and  more  rarely  brown  green  are 
the  prevailing  colors.  It  is  commonly  crystallized  in  three-  and  six- 
sided  prisms  and  columns,  generally  arranged  in  radial  groups.  As 
a rule  the  columns  are  aggregated  together,  and  it  is  therefore  usually 
difficult  or  impossible  to  distinguish  the  geometric  form  of  indi- 
vidual crystals.  Tourmaline  has  a specific  gravity  of  3,  or  less  than 
half  that  of  cassiterite.  This  property  and  its  form,  wffiere  discern- 
ible, are  its  most  characteristic  differences  from  cassiterite,  with 
which  it  has  frequently  been  confounded. 

Muscovite. — White  mica  occurs  at  Ear  Mountain  in  granite  tongues 
extending  from  the  central  mass  out  into  the  surrounding  sedimen- 
tary rocks. 

Zinnwaldite. — The  lithium-iron  mica,  zinnwaldite,  occurs  abun- 
dantly in  the  cassiterite  veinlets  on  Cassiterite  Creek,  and  is  habitually 
associated  with  topaz  and  fluorite.  It  resembles  muscovite,  both  to 
the  eye  and  under  the  microscope,  but  differs  from  it  by  possessing  a 
smaller  axial  angle.  It  fuses  readily  to  a black  magnetic  globule. 
(For  analysis  see  p.  54.) 

Biotite. — The  granites  of  the  region  contain  black  mica  as  a sub- 
ordinate constituent  in  the  form  of  small  lustrous  plates.  It  occurs 
also  in  a pegmatite  on  Brooks  Mountain,  in  plates  up  to  one-half  inch 
in  size. 

Phlogopite. — Phlogopite,  the  magnesia  mica,,  is  found  as  small 
flakes  associated  with  vesuvianite  in  contact-metamorphosed  lime- 
stone on  Brooks  Mountain,  and  with  tremolite  is  abundant  in  the 
limestone  east  of  Tin  City. 

Chlorite. — Chlorite  is  common  in  the  gieenstone  of  the  slate  area 
near  York. 

Kaolin. — Kaolin  occurs  abundantly  as  an  alteration  product  in  the 
Cassiterite  lode. 


MINERALOGY  OF  THE  REGION. 


23 


Apatite. — Apatite  occurs  as  a microscopic  constituent  of  the 
granites. 

Ludwigite  (3Mg0.B203-f-Fe0.Fe203). — A finely  fibrous  dark- 
green  mineral,  soluble  in  hydrochloric  acid,  forms  small  radial  aggre- 
gates in  a contact-metamorphosed  limestone  from  Brooks  Mountain. 
It  gives  a decided  flame  reaction  for  boron,  and  is  therefore  tentatively 
identified  as  ludwigite. 

Paigeite. — The  new  boron-tin  mineral,  paigeite,®  was  found  at  two 
localities,  near  Bead’s  cabin  on  Brooks  Mountain  in  loose  blocks  and 
at  Ear  Mountain  in  situ.  The  Brooks  Mountain  material  is  inter- 
grown  with  vesuvianite,  calcite,  and  hedenbergite,  with  subordinate 
biotite  and  arsenopyrite  in  sporadic  grains.  At  Ear  Mountain  it 
occurs  evenly  disseminated  through  a tourmaline-lime-silicate  horn- 
fels  consisting  essentially  of  calcite,  tourmaline,  vesuvianite,  fluorite, 
and  zoisite,  with  accessory  phlogopite,  chalcopyrite,  and  magnetite. 
It  is  a lustrous  coal-black  foliated  mineral,  and  has  a hardness  of 
about  3,  with  a density  of  4.71.  Analysis  of  material  from  Brooks 
Mountain  gave  the  following  result,  which  is  recalculated  on  the 
basis  of  100  per  cent ; it  contains  probably  15  per  cent  Sn02 : 


Analysis  of  paigeite  from  Brooks  Mountain. 


FeO 

MgO 

Fe203 

H20_ 

Sn02 

B203 


51.99 
1.  68 
19.  54 
2.  37 

24.  42 


100.  00 


Hulsite? — On  the  northwestern  flank  of  Brooks  Mountain  a pros- 
pect cut  has  been  opened  on  a showing  of  contact-metamorphic  min- 
erals occurring  in  a marmorized  limestone  10  feet  from  the  granite 
contact.  Examination  of  this  deposit  indicated  that  an  unknown 
mineral,  which  subsequent  investigation  proved  to  be  a new  boron-tin 
mineral,  was  present  in  considerable  abundance.  Hulsite,  as  the  min- 
eral was  named,  is  closely  associated  with  magnetite  and  a boron 
vesuvianite  in  a matrix  of  coarse  calc  spar,  in  which  garnet  and  fluor- 
ite occur  in  subordinate  amounts.  The  characteristic  features  of  the 
new  mineral  are  its  strong  submetallic  luster,  black  color,  good  cleav- 
age after  the  prism  of  57°  38',  and  tendency  toward  a tabular 
development.  Its  hardness  is  about  3;  density,  4.28.  It  contains 
probably  20  per  cent  Sn02.c 

° Knopf,  A.,  and  Schaller,  W.  T.,  Two  new  boron  minerals  of  contact-metamorphic 
origin  : Am.  Jour.  Sci.,  4th  ser.,  vol.  25,  1908,  p.  323. 

6 Op.  cit,  p.  323. 

c Chemical  work  is  at  present  in  progress  by  W.  T.  Schaller,  with  a view  to  determin- 
ing the  formulae  of  hulsite  and  paigeite.  It  appears  that  the  original  determinations  of 
B203  were  defective,  so  that  the  formulae  proposed  are  untenable. 


24 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


Wolframite  (Fe,MnW04;  76.4  per  cent  tungsten  trioxide). — The 
valuable  mineral  wolframite  occurs  associated  with  cassiterite  on 
Cassiterite  Creek  and  with  galena  and  stannite  in  a topaz-fluorite 
gangue  on  the  Oregon  claim  on  Lost  River.  Its  distinguishing  fea- 
tures are  its  great  weight  (specific  gravity,  7.3),  black  color,  and 
brilliant  submetallic  luster  on  fine  cleavage  surfaces.  Its  hardness  is 
5.5,  which  means  that  it  can  be  rather  readily  scratched  with  a knife. 
The  resemblance  of  wolframite  to  the  iron-rich  zinc  blend  of  Brooks 
Mountain  has  already  been  pointed  out. 

S cheelite  (CaW04;  80.6  per  cent  tungsten  trioxide). — The  mineral 
scheelite  has  been  detected  as  a microscopic  constituent  of  certain 
lime — silicate  contact  rocks  of  Cape  Mountain.  It  was  also  found  as 
minute  grains  in  a number  of  small  cassiterite  veinlets  on  Cassiterite 
Creek  and  in  the  altered  limestone  adjoining  the  veinlets.  As  an  al- 
teration product  it  forms  microscopic  coatings  around  wolframite 
crystals.  None  of  these  occurrences  are  of  possible  commercial  im- 
portance. Scheelite  is  a heavy  white  mineral  of  vitreous  luster, 
having  a specific  gravity  of  6 and  a hardness  ranging  from  4.5  to  5. 

ECONOMIC  GEOLOGY. 

OUTLINE. 

Tin  ore  occurs  in  both  lode  and  placer  form,  but  up  to  the  present 
time  practically  the  only  production  has  been  from  the  placers  of 
a single  stream — Buck  Creek.  Placer  tin  is  known  to  be  widely 
distributed  in  the  streams  of  Seward  Peninsula,®  and  has  been  found 
in  some  of  the  gold  placers  near  Nome,  but  in  amounts  that  are  com- 
mercially unprofitable. 

Cassiterite  is  the  only  mineral  that  is  likely  to  prove  of  economic 
value  as  a source  of  tin.  Stannite  is  also  known  to  occur,  but  at  one 
locality  only,  where  it  is  associated  with  galena  in  a remarkable 
argentiferous  wolframite-topaz  ore.  Two  new  tin  minerals  (mag- 
nesian iron-tin  borates)  have  been  discovered,  but  on  account  of  their 
low  tin  content  (approximately  15  per  cent  Sn02)  are  probably  not 
worth  exploitation. 

The  lode-tin  deposits  are  genetically  associated  with  the  granitic 
intrusives,  and  on  account  of  the  abundance  of  limestone  in  the  region 
llie  Seward  Peninsula  tin  occurrences  possess  a number  of  unique  and 
distinctive  features.  A variety  of  pneumatolytic  contact  rocks  have 
been  produced  around  the  margins  of  the  granites,  and  certain  of 
these  contain  the  iron-tin  borates  (hulsite  and  paigeite)  as  essential 
constituents.  The  resemblance  of  numerous  heavy  contact-meta- 

a Collier,  A.  ,T.,  Recent  developments  of  Alaskan  tin  deposits  : Bull.  U.  S.  Geol.  Survey 
No.  250,  1005,  p.  127. 


ECONOMIC  GEOLOGY. 


25 


morphic  minerals,  such  as  garnet,  to  cassiterite,  coupled  with  the  fact 
that  some  of  the  contact-metamorphic  rocks  are  actually  stanniferous, 
has  led  to  much  prospecting  along  the  granite-limestone  contacts. 
Only  one  contact  rock  containing  cassiterite  in  amounts  appreciable 
under  the  microscope  was  found,  however,  during  the  course  of  the 
present  investigation. 

Tin-bearing  rock  occurs  also  in  tourmalinized  granite,  in  fractured 
quartz  porphyry  dikes  cutting  limestone,  and  in  the  adjoining  lime- 
stone itself,  intergrown  with  danburite,  tourmaline,  tremolite,  and 
topaz.  Cassiterite  is  found  in  quartz  stringers  in  granite,  in  slate, 
and  in  limestone,  accompanied  by  an  intense  metasomatism.  Yeinlets 
in  limestone  may  consist  wholly  of  cassiterite,  topaz,  zinnwaldite, 
and  fluorite.  In  the  slate  area  cassiterite  also  occurs  embedded  in 
tabular  masses  of  radial  actinolite  which  appear  to  be  interstratified 
with  horizontal  slates. 

Most  of  the  prospects  have  been  but  imperfectly  opened.  Some 
are  of  promising  character,  but  from  the  point  of  view  of  the  con- 
servative mining  man  their  value  is  yet  to  be  demonstrated. 

Each  of  the  four  localities  at  which  lode  tin  is  being  prospected — 
Ear  Mountain,  Buck  Creek,  Cape  Mountain,  and  Lost  River — shows 
certain  distinctive  features,  so  it  has  been  found  advisable  to  describe 
them  separately  in  geographic  order,  as  enumerated.  To  these  has 
been  added  Brooks  Mountain,  on  which  some  stanniferous  contact- 
metamorphosed  limestone  has  been  found,  though  no  cassiterite-bear- 
ing  rock  has  yet  been  discovered  there. 

LODES. 

EAR  MOUNTAIN. 

INTRODUCTION. 

Ear  Mountain  is  located  in  the  northwestern  part  of  Seward  Penin- 
sula, in  latitude  66°  north  and  longitude  16G°  west.  It  is  50  miles 
north  of  Teller  and  15  miles  south  of  Shishmaref  Inlet,  a large,  shal- 
low embayment  from  the  Arctic  Ocean.  The  region  is  not  readily 
accessible,  and  with  the  present  means  of  communication  it  is  prac- 
tically impossible  to  bring  in  supplies  during  the  summer  months. 
Steamers  of  light  draft  do  not  venture  to  approach  nearer  than 
within  H miles  of  Sarichef  Island,  at  the  mouth  of  Shishmaref  Inlet, 
though  gasoline  schooners  make  landings  directly  on  the  island. 
The  inlet  itself  is  not  navigable  other  than  by  oomiaks  and  flat- 
bottomed  dories.  The  first  steamer  of  the  season  of  190T  bound  for 
arctic  points  passed  northward  through  Bering  Strait  on  July  2. 
At  this  time  the  last  ice  floes  from  the  spring  break-up  were  drifting 
out  of  Shishmaref  Inlet. 


26 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


Ear  Mountain  has  long,  smooth  slopes  on  the  north  and  east  sides, 
but  on  the  south  and  west  sides  rises  abruptly  above  the  tundra- 
covered  plateau  from  an  elevation  of  1,000  feet  to  a maximum  of  2,308 
feet  above  sea  level.  The  mountain  possesses  two  flat-topped  sum- 
mits, of  which  the  southern  is  slightly  the  higher.  Two  great  granite 
monoliths  rest  upon  the  broad  northern  summit,  and  are  visible,  but 
as  very  diminished  objects,  from  ships  on  the  Arctic  Ocean,  20  miles 
distant.  They  were  noted  by  the  early  navigators,  and  from  them  the 
mountain  received  its  rather  fanciful  name. 

Cassiterite  in  the  form  of  stream  tin  was  accidently  discovered  on 
Eldorado  Creek,  on  the  northeast  side  of  the  mountain,  in  1901.  Nug- 
gets several  inches  in  diameter  can  be  picked  off  the  bed-rock  riffles 
of  this  stream,  but  on  account  of  the  small  body  of  gravel  the  creek 
offers  no  placer  possibilities.  The  bed-rock  source  of  this  cassiterite 
has  not  yet  been  discovered.  None  of  the  rocks  that  are  being  pros- 
pected show  visible  cassiterite,  and  only  a few  show  small  amounts 
microscopically.  Attention  has  lately  been  directed  to  some  occur- 
rences of  chalcopyrite  and  galena  found  in  contact-metamorphic  rock. 


GENERAL  GEOLOGY. 


The  rocks  flanking  Ear  Mountain  are  prevailingly  of  a calcareous 
character,  and  comprise  contorted  limestone  and  lime-mica  schists. 
On  the  south  side  of  the  mountain  some  black  siliceous  schists  appear. 
Intrusive  into  these  sedimentary  rocks  and  forming  the  core  of  Ear 
Mountain  is  a large  mass  of  coarsely  crystalline  granite  from  which 
numerous  apophyses  of  fine-grained  white  granite  extend  into  the 
surrounding  sedimentary  rocks.  (See  figs.  2 and  3.)  The  limestones 
were  highly  susceptible  to  contact  metamorphism  and  succeeded  to  an 
unusual  extent  in  fixing  the  magmatic  emanations  in  such  minerals  as 
tourmaline,  axinite,  paigeite  (a  magnesian  iron-tin  borate),  fluorite, 
scapolite,  galena,  and  chalcopyrite. 

The  youngest  rocks  of  the  region  occur  as  quartz-augite  porphyry 
dikes  cutting  both  limestone  and  granite.  The  two  most  prominent 
of  these  dikes  are  15  feet  thick  and  can  be  traced  for  several  thousand 
feet,  striking  N.  30°  E.  and  north  and  south  (magnetically). 

Granite . — The  granite  of  Ear  Mountain  consists  of  feldspar  (ortho- 
clase  with  subordinate  amounts  of  oligoclase-albite  and  microperth- 
ite),  quartz,  and  biotite.  Both  quartz  and  feldspar  tend  to  assume 
idiomorphic  forms,  even  in  the  coarsest  grained  phases.  The  quartz 
is  smoky,  and  has  not  infrequently  been  mistaken  by  the  prospector 
for  cassiterite,  especially  where  the  color  was  more  intense.  Near  the 
contacts  the  granite  is  finer  grained,  and  is,  in  many  places,  a typical 
granite  porphyry.  In  the  central  portion  of  the  main  granite  body 
a small  area  of  this  type  of  rock  was  found,  but  whether  it  represents 


ECONOMIC  GEOLOGY. 


27 


a mere  variation  in  texture  or  a separate  intrusion  could  not  be  deter- 
mined. Black  tourmaline  is  common  in  the  granite  of  Ear  Moun- 
tain, but  is  always  associated  with  seams  consisting  of  quartz  and 


Contour  interval  200  feet 


Silts  and  gravels  Limestone  and  schist  Granite  Quartz-augite  porphyry 

Fig.  2. — Geologic  sketch  map  of  Ear  Mountain. 

tourmaline,  and  adjoined  by  bands  of  tourmalinized  granite  2 or  3 
inches  broad.  The  quartz-tourmaline  seams,  on  account  of  their  re- 
sistance to  atmospheric  attack,  weather  out  in  relief.  Several  such 

FEET 
2300 

1800 

1300 

800 


Fig.  3. — Geologic  section  through  Ear  Mountain. 


s i V 

r-O/jr'- 

Is  \ / V/l M 

r 

seams  can  be  seen  running  up  and  down  the  “ Ears  ” — the  granite 
monoliths  from  which  the  mountain  was  named. 


28 


TTN  DEPOSITS  OF  SEWAED  PENINSULA,  ALASKA. 


The  offshoots  from  the  main  granite  body  are  finer  grained  and 
lighter  colored.  They  contain,  besides  quartz  and  feldspar,  white 
mica,  and  in  many  places  numerous  small  prisms  of  tourmaline,  evenly 
distributed  throughout  the  body  of  the  rock  and  unconnected  with 
the  presence  of  seams.  In  addition  to  the  constituents  visible  to  the 
unaided  eye,  the  microscope  shows  a small  amount  of  topaz.  Some 
fluorite  is  associated  with  the  muscovite,  which,  like  the  topaz,  occurs 
in  skeletal  growths.  Minute  cassiterite  prisms  surrounded  by  pleo- 
chroic  halos  occur  embedded  in  the  muscovite.  The  tourmaline, 
which  is  brown,  usually  occurs  in  discrete  prisms,  but  may  also  form 
skeletal  growths.  The  three  minerals — muscovite,  topaz,  and  tourma- 
line— were  formed  after  the  feldspar  and  quartz,  and  apparently  by 
similar  processes.  They  are  absent  from  the  granite  of  the  main 
mass,  and  indicate  an  enrichment  of  fluorine  and  boron  in  the 
apophyses. 

Contact  metamorphism. — An  extensive  development  of  lime-silicate 
hornfels,  rich  in  the  so-called  pneumatolytic  minerals,  has  been  pro- 
duced around  the  periphery  of  the  granite  mass.  The  limestones 
that  were  metamorphosed  were  originally  impure  limestones  irregu- 
larly laminated  with  thin  bands  (one-eighth  to  one-fourth  inch 
thick)  of  argillaceous  material.  The  contact  metamorphism  has  con- 
sisted in  part  in  a recrystallization  of  the  sedimentary  material  and 
in  part  in  an  accession  of  new  material  by  magmatic  emanations. 

The  simplest  case  of  contact  metamorphism  is  that  of  the  tourma- 
linized  limestone  formed  on  the  south  side  of  Eldorado  Creek.  Here 
the  argillaceous  laminae  have  been  converted  into  black  tourmaline 
and  the  calcareous  bands  have  been  marmorized,  producing  a rock 
resembling  a gneiss.  The  tourmaline  is  pleochroic  in  tones  of  blue 
and  green.  Tremolite  has  also  been  developed,  with  diopsicle  and 
vesuvianite  in  minor  amounts.  At  other  points  along  the  contact 
the  original  banded  character  of  the  limestone  is  preserved,  and  even 
emphasized,  by  the  production  of  trains  of  vesuvianite  crystals.  On 
Quartz  Creek  the  limestones  have  been  converted  into  pyroxene- 
scapolite  hornfels.  A prospect  cut  at  this  locality  exposes  a dark- 
colored  rock,  evenly  flecked  with  a lustrous  coal-black  lamellar 
mineral,  which  subsequent  investigation  has  shown  to  be  a new 
boron-tin  mineral,  and  which  has  been  named  paigeite.® 

In  addition  to  the  paigeite,  considerable  tourmaline  and  minor 
amounts  of  chalcopyrite  and  magnetite  are  visible.  Under  the  micro- 
scope the  rock  resolves  itself  into  a confused  intergrowtli  of  zonally 
banded  tourmaline,  calcite,  vesuvianite,  zoisite,  paigeite,  fluorite,  and 
accessory  phlogopite,  chalcopyrite,  and  magnetite.  The  paigeite  is 
embedded  in  the  various  other  constituents  in  trichite-like  forms, 


Am.  Jour.  Sci.,  4th  sei\,  vol.  25,  1908,  p.  323. 


ECONOMIC  GEOLOGY. 


29 


many  of  which  are  of  capillary  dimensions,  and  in  matted  aggregates 
of  fibers  (PI.  II,  A).  Closely  associated  with  this  paigeite  hornfels  is 
a tourmaline-pyroxene-sca polite  hornfels,  which  reacts  chemically  for 
chlorine.  A prospect  opening  at  the  granite-limestone  contact  near 
Tuttle  Creek  reveals  a tourmaline-axinite  hornfels.  The  axinite  is 
of  highly  vitreous  appearance  and  of  light-brown  color,  and  is  there- 
fore readily  recognizable  in  the  hand  specimen.  It  reacts  for  boron 
and  manganese.  In  thin  section  it  is  colorless  with  faint  blue  pleo- 
chroisms,  but  shows  no  recognizable  cleavage,  although  agreeing 
otherwise  in  its  optical  properties  with  those  cited  by  Rosenbusch. 
Tourmaline  is  quantitatively  more  important  than  the  axinite  in 
this  hornfels.  It  is  subliedral  and  in  numerous  places  zonally  banded, 
with  pleochroism  varying  from  blue  to  green.  In  addition  to  the 
tourmaline  and  axinite,  actinolite,  pyroxene,  quartz,  fluorite,  and 
calcite  are  confusedly  intergrown,  though  the  last  three  minerals 
occur  rather  in  minor  amounts.  Some  cassiterite  is  found  embedded 
in  the  other  constituents  in  grains  large  enough  to  allow  its  optical 
identification  beyond  question.  This  tourmaline-axinite  hornfels  is 
the  only  contact-metamorphic  rock  containing  cassiterite  found  in  the 
entire  Alaskan  tin  region,  although  a large  number  of  such  rocks  were 
examined  on  account  of  the  prevalent  belief  that  they  are  tin  bearing. 

Quartz-augite  porphyry  dikes. — The  quartz-augite  porphyry  dikes 
consist  of  a dense-textured  rock  of  dark-blue  or  green  color  contain- 
ing numerous  phenocrysts  of  feldspar  and  smoky  quartz,  with  lesser 
amounts  of  augite  and  biotite.  The  augites  attain  unusually  large 
dimensions — as  much  as  2 inches  or  more — and  are  commonly  re- 
garded as  “ tin  crystals  ” by  the  local  prospectors.  The  presence  of 
these  augite  phenocrysts  thus  mistaken  for  cassiterite  has  led  to  con- 
siderable prospecting  of  the  quartz  porphyry  dikes.  In  thin  section 
the  quartz  phenocrysts  are  seen  to  be  corroded  and  embayed;  the 
plagioclase,  which  corresponds  to  bytownite  (Ab25An75),  is  also  cor-^ 
roded.  Augite  and  biotite  are  rare.  The  groundmass  consists  of 
plagioclase  laths  approximating  Ab40An60  in  composition,  and  they 
are  disposed  in  fluxional  arrangement.  Apatite  is  unusually  abun- 
dant. According  to  this  characterization  the  dikes  are  augite  dacites. 
Calcite  and  tourmaline  are  common  as  secondary  minerals.  Where 
tourmalinization  has  been  more  intense  fluorite,  arsenopyrite,  and 
cassiterite  appear. 

Two  periods  of  tourmalinization  can  therefore  be  distinguished — 
one  contemporaneous  with  the  contact  metamorphism  and  one  follow- 
ing the  intrusion  of  the  augite  dacite  dikes.  That  a considerable 
lapse  of  time  separated  these  periods  is  indicated  by  the  fact  that 
the  granite  nowT  exposed  to  view  had  become  thoroughly  cooled 
during  this  interval  and  was  able  to  chill  the  later  intrusives. 


30 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


MINERAL  OCCURRENCES. 

In  addition  to  vesuvianite,  tourmaline,  axinite,  and  other  contact- 
metamorphic  minerals,  the  contact  rocks  at  certain  localities  are 
flecked  with  galena,  chalcopyrite,  and  a lustrous  coal-black  iron-tin 
borate,  which  has  been  named  paigeite.  It  is  this  type  of  rock  which 
has  raised  hopes  that  copper  and  lead  deposits  of  economic  value 
exist  at  Ear  Mountain.  Cassitente-bearing  rock  also  is  believed 
by  the  prospector  to  occur  along  the  contact  at  many  points. 

The  practical  importance  of  understanding  how  the  deposits  were 
formed  arises  from  the  following  considerations: 

(1)  That  the  size  and  persistence  of  the  deposits  are  dependent 
on  the  mode  of  origin. 

(2)  That  their  probable  value,  besides  being  affected  by  the  size 
and  persistence  of  the  deposit,  is  also  dependent  on  the  mode  of 
origin. 

Under  the  first  heading  attention  may  be  drawn  to  certain  struc- 
tural features  of  the  granite  boss  of  Ear  Mountain — features  which 
also  occur  at  Cape  Mountain  and  at  Brooks  Mountain.  It  can  be 


s 


Fig.  4. — Diagrammatic  section  at  Eunson’s  shaft,  Ear  Mountain. 


shown  from  various  lines  of  evidence  that  any  such  granite  mass  as 
that  of  Ear  Mountain  must  have  cooled  under  a considerable  blanket 
of  protecting  rocks.  The  surface  of  the  granite  against  these  over- 
lying  rocks  is  not  necessarily  smooth,  but  may  be  of  gently  undu- 
lating character,  or  may  even  be  furrowed  by  sharp  ridges,  such  as, 
for  instance,  have  been  revealed  by  the  extensive  mining  operations 
in  Cornwall.  The  troughs  or  depressions  between  these  granite 
ridges  will  be  occupied  by  the  overlying  rocks,  which  will  therefore 
appear  immersed  beneath  the  general  surface  of  the  granite.  At 
Ear  Mountain  erosion  has  proceeded  far  enough  to  strip  off  much 
of  the  protective  capping  of  sedimentary  rocks  which  formerly 
arched  over  the  granite,  though  on  the  highest  peak — the  south 
peak — the  granite  is  still  covered  by  a thickness  of  100  feet  of  schists 
and  sheared  greenstone.  This  erosion  has  revealed  the  fact  that 
the  former  surface  of  the  granite  boss  was  slightly  uneven.  The 
limestones  and  schists  resting  in  the  inequalities  now  occur  as  iso- 
lated patches  surrounded  on  all  sides  by  granite.  A section  across 
Ear  Mountain  (fig.  4)  illustrates  this  feature.  These  rocks  may 


ECONOMIC  GEOLOGY. 


31 


show  locally  indications  of  ore,  but  the  rock,  being  of  contact- 
metamorphic  origin,  will  have  a small  areal  extent,  will  have  no 
great  depth,  and  will  give  out  when  the  underlying  surface  of  the 
granite  is  reached.  The  prospector,  therefore,  should  use  consider- 
able caution  before  attempting  any  exploitation  of  ore  bodies  occur- 
ring in  such  patches  of  rock  lying  upon  the  surface  of  the  granite. 

Along  the  periphery  of  the  granite  the  ore  deposits  of  contact- 
metamorphic  origin  are  more  likely  to  have  permanence  in  depth. 
What  is  known  of  contact-metamorphic  deposits  in  other  parts  of 
the  world,  however,  is  not  of  a character  to  encourage  extravagant 
hopes  for  the  similar  occurrences  found  at  Ear  Mountain.  They  are 
usually  of  low  grade  and  irregular  in  form.  Such  deposits  are 
mined  in  southeastern  Alaska  for  their  copper  content,  but  condi- 
tions must  be  exceptionally  favorable  to  make  them  of  commercial 
value. 

On  the  northeastern  side  of  the  mountain,  near  Vatney’s  cabin, 
where  the  contact  metamorphism  has  been  more  pronounced  than 
usual,  some  metamorphosed  limestone  in  proximity  to  a granite  dike 
was  being  prospected  for  tin  ore.  It  contains  small  bunches  of  a 
reddish-brown  mineral  showing  crystal  faces,  which,  when  carefully 
examined,  are  seen  to  be  diamond  shaped.  This  is  typical  of  garnet. 
When  only  the  apex  of  the  garnet  crystal  is  visible  it  bears  an  exceed- 
ingly deceptive  resemblance  to  the  four-sided  pyramid  characteristic 
of  cassiterite. 

Near  Tuttle  Creek  a prospect  trench  has  been  opened  to  uncover 
some  contact-metamorphosed  limestone  at  the  granite  contact.  The 
stanniferous  tourmaline-axinite  hornfels  whose  microscopic  features 
have  already  been  described  occurs  at  this  locality,  but  no  cassiterite 
is  visible  in  the  rock  to  the  unaided  eye.  The  microscope,  however, 
shows  the  presence  of  a small  fraction  of  1 per  cent — an  amount  too 
small,  in  view  of  the  nature  of  the  deposit  and  the  remoteness  of  the 
region,  to  give  rise  to  any  extensive  hopes  that  commercial  bodies  of 
cassiterite  exist  along  the  contact. 

The  quartz-tourmaline  seams  that  cut  the  granite  have  already 
been  described.  At  various  places  on  Ear  Mountain  interlacing  net- 
works of  such  seams  occur,  and  an  extensive  tourmalinization  of  the 
■ adjoining  granite  has  taken  place.  Masses  of  quartz-tourmaline  rock 
have  been  produced,  little  resembling  the  original  granite.  Such  oc- 
currences have  been  opened  by  shallow  prospect  pits  at  a number  of 
points.  It  is  quite  possible  that  some  deposits  of  this  character  may 
carry  low-grade  values  in  tin,  but  those  opened  thus  far  lend  small 
encouragement  to  this  idea. 

On  the  northeast  side  of  Ear  Mountain  an  augite-quartz  porphyry 
dike  has  been  opened  by  a shaft  and  explored  by  a drift  112  feet  long. 


32 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


Nothing  but  hard,  barren  rock  was  encountered.  Work  was  sus- 
pended, and  at  the  time  of  visit  the  shaft  was  flooded  with  water. 
F arther  southwest  on  the  extension  of  the  same  dike  a number  of  open 
cuts  have  been  made  on  account  of  the  prevalence  of  numerous  large 
augite  crystals  embedded  in  the  dike  rock.  Chemical  analyses  of 
“ ore  ” samples,  made  in  the  laboratory  of  the  Survey,  show  the  pres- 
ence of  only  traces  of  tin,  amounting  to  a few  hundredths  of  1 per 
cent. 

A shaft  known  as  Eunson’s  shaft  (fig.  4)  was  sunk  near  the  point 
where  a quartz  porphyry  dike  striking  north  and  south  crosses  the 
granite-limestone  contact.  The  shaft  was  reported  to  be  30  feet  deep, 
but  at  the  time  of  visit  was  flooded  with  water  and  partly  caved  in. 
On  the  dump  a variety  of  rock  is  represented.  Contact-metamor- 
phosed limestone,  granite,  granite  porphyry,  quartz  porphyry,  and 
various  altered  modifications  of  the  quartz  porphyry  appear.  The 
quartz  porphyry  is  partly  tourmalinized  and  contains  small  patches 
of  purple  fluorite,  abundant  arsenopyrite,  and  microscopic  grains  of 
cassiterite.  The  tin  ore  reported  from  this  locality  probably  came 
from  highly  altered  portions  of  the  quartz  porphyry  dike. 

BUCK  CREEK. 

GEOLOGIC  FEATURES. 

The  Buck  Creek  area  is  a part  of  the  slate  belt  previously  described. 
The  bed  rock  consists  of  fine-textured  arenaceous  slates,  usually  lying 
flat.  Along  Buck  Creek  the  rocks  do  not  display  a highly  meta- 
morphosed aspect,  but  are  in  large  part  shalelike,  associated  with 
beds  of  banded  yellowish  fine-grained  sandstone  and  bluish  kaolinic 
sandstone.  The  slaty  cleavage,  however,  is  developed  in  an  irregular 
and  variable  degree  in  different  parts  of  the  area.  At  the  head  of 
Sutter  Creek  the  arenaceous  banded  rock  is  thinly  fissile,  with  the 
cleavage  at  right  angles  to  the  sedimentary  banding.  Greenstones 
of  diabasic  character  occur  with  the  slates,  but  can  rarety  be  found 
in  place.  A prominent  exposure,  however,  forms  a low  ridge  im- 
mediately to  the  north  of  Buck  Creek. 

Two  quartz  porphyry  dikes  cut  the  slates  at  the  head  of  Buck 
Creek  The  characteristic  feature  of  these  dikes,  especially  of  the 
one  extending  northward  from  Potato  Mountain,  is  the  abundance 
of  large  quartz  phenocrysts,  many  of  them  smoky,  embedded  in  a 
dense  light-gray  matrix.  The  feldspars  are  less  conspicuous.  The 
margins  of  the  dikes  have  been  strongly  chilled,  and  show  a bluish- 
black  rock  containing  small  phenocrysts  of  quartz  and  feldspar.  On 
the  summit  of  Potato  Mountain  the  dike  is  but  1 foot  thick  and  con- 
sists entirely  of  this  kind  of  rock.  Farther  north  the  thickness 


ECONOMIC  GEOLOGY. 


33 


increases  to  10  feet.  The  other  quartz  porphyry  dike,  which  trends 
N.  34°  W.  (magnetic),  has  a maximum  thickness  of  50  feet  and  a 
length  of  several  thousand  feet.  These  are  the  only  acidic  igneous 
intrusives  known  in  the  region. 

ECONOMIC  GEOLOGY. 

Cassiterite  occurs  in  three  ways  in  the  bed  rock  of  the  Buck  Creek 
area — (1)  as  an  impregnation  in  quartz  porphyry  dikes,  (2)  in 
quartz  stringers  cutting  the  slates,  and  (3)  intergrown  with  arsenopy- 
rite  in  a gangue  of  radial  actinolite.  Development,  however,  has  not 
yet  proceeded  far  enough  to  demonstrate  the  commercial  importance 
of  any  of  these  occurrences. 

At  numerous  points  on  the  ridge  of  hills  at  the  head  of  Buck  Creek 
open  cuts  have  made  made,  exposing  networks  of  quartz  stringers  in 
the  slates.  The  veinlets  are  usually  a few  inches  thick,  and  here  and 
there  contain  cassiterite.  Some  merely  show  rosettes  of  blue  tourma- 
line or  are  barren.  Gold  is  probably  present  in  some  of  them,  as 
placer  gold  is  found  in  the  stream  tin  of  Buck  Creek.  On  the  divide, 
at  an  altitude  of  1,140  feet,  a prospect  pit  discloses  a fine  showing  of 
tin  quartz.  The  hole  is  10  feet  deep  and  exposes  a face  of  7 feet  of 
quartz  carrying  a considerable  percentage  of  cassiterite.  The  develop- 
ments are  inadequate  to  give  either  dip  or  strike  of  the  ore  body  with 
any  degree  of  certainty,  nor  is  its  linear  persistence  known.  The  depth 
attained  is  not  great  enough  to  expose  solid  bed  rock,  and  the  walls  are 
consequently  still  in  a highly  shattered  condition  due  to  the  heave  of 
the  frost.  The  ore  is  a milk-white  quartz  of  greasy  luster,  and  contains 
cassiterite  disseminated  through  it  in  crystalline  aggregates,  intimately 
intergrown  with  arsenopyrite  and  small  needles  of  blue  tourmaline. 
In  thin  section  the  tourmaline  is  found  to  be  light  blue  in  color,  the 
pleochroism  varying  from  clear  blue  to  colorless  (alkali  tourmaline). 
The  slate  wall  rock  has  a greenish  cast,  and  under  the  microscope  is 
found  to  consist  almost  entirely  of  minute  tourmaline  prisms  in  par- 
allel orientation,  with  a small  amount  of  interstitial  feldspar.  The 
bright  boron  flame  which  the  slate  yields  when  treated  with  fluorite 
mixture  abundantly  confirms  the  microscopic  diagnosis.  About  GO 
feet  from  the  prospect  pit  the  outcrops  consist  of  normal  arenaceous 
slate  lying  nearly  horizontal. 

At  the  head  of  Peluk  Creek  (a  small  tributary  of  Buck  Creek)  a 
shaft,  reported  to  be  20  feet  deep,  was  sunk  on  quartz  stringers  in  the 
slate.  'The  material  on  the  dump  shows  abundant  pyrite  and  a little 
cassiterite.  In  the  same  general  vicinity  float  tin  ore  has  been  dis- 
covered in  which  the  cassiterite  occurs  in  totally  different  paragenetic 
association.  It  is  found  embedded  in  a green  rock  composed  of  radi- 
ating groups  of  actinolite.  Relatively  large  amounts  of  arsenopyrite 


54356— Bull.  358—08 3 


34  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

are  usually  intergrown  with  the  cassiterite.  A number  of  open  cuts 
have  been  made  in  the  effort  to  locate  the  bed-rock  source  of  this  tin- 
bearing rock.  At  time  of  visit  the  owner  of  the  property  had 
just  succeeded  in  uncovering  the  edge  of  the  deposit  in  place,  so  that 
few  facts  are  available  as  to  its  geologic  relations  and  probable  value. 
Where  exposed  it  was  highly  oxidized,  and  apparently  represented  a 
tabular  mass  intercalated  between  horizontal  slates.  In  thin  section 
the  ore  rock  consists  of  sheaf-like  bundles  of  actinolite,  with  which 
some  finely  granular  calcite  is  associated.  A small  amount  of  quartz 
occurs  in  the  immediate  vicinity  of  the  cassiterite,  and  both  these 
minerals  are  transfixed  by  needles  of  actinolite  (PL  III,  A).  Tour- 
maline in  the  form  of  a few  small  prisms  occurs  as  an  accessory 
mineral.  The  slate  in  contact  with  the  stanniferous  rock  is  of  a 
dense,  poorly  fissile  variety.  Under  the  microscope  it  shows  no  de- 
cided evidence  of  metasomatic  alteration.  It  contains  abundant  mag- 
netite disseminated  through  it  in  minute  grains,  which  may  possibly 
be  of  epigenetic  origin. 

At  a number  of  points  the  quartz  porphyry  dikes  are  'somewhat 
impregnated  with  pyrite,  especially  in  the  vicinity  of  seams.  A 
small  amount  of  tourmaline  in  radial  groups  appears,  and  white 
mica  replaces  the  feldspar  phenocrysts.  Specimens  containing  a 
small  amount  of  cassiterite  have  been  obtained,  but  appear  to  be  of 
extremely  rare  occurrence.  The  largest  quartz  porphyry  dike  has 
been  faulted  approximately  400  feet  in  a north  and  south  direction. 
The  line  of  this  fault  is  marked  by  a great  quartz  vein  15  feet  or  more 
in  thickness,  which  can  be  traced  for  considerably  over  a mile.  The 
vein  contains  a vast  number  of  slate  fragments,  each  of  which  has 
acted  as  a nucleus  around  which  quartz  crystals  commenced  to  grow. 
Failure  of  the  crystals  to  coalesce  in  their  outer  extremities  has  pro- 
duced a vuggy  vein  lined  with  innumerable  hexagonal  pyramids  of 
quartz.  No  mineral  except  some  botryoidal  limonite  incrusting  the 
quartz  crystals  has  been  observed  in  the  vein,  so  that  it  is  without 
economic  importance.  Whether  the  formation  of  this  vein  was  con- 
temporaneous with  that  of  the  stanniferous  quartz  veinlets  is  of  con- 
siderable practical  interest.  If  of  the  same  period  of  origin  there  is 
a strong  possibility  that  persistent  tin-quartz  veins  may  yet  be  found 
in  the  slate  area. 

ORIGIN  OF  THE  ORES. 

The  developments  and  exposures  are  entirely  too  inadequate  to 
allow  a very  extended  discussion  of  the  origin  of  the  ores.  From 
analogy  with  the  Lost  River  area,  however,  it  is  believed  that  a gran- 
ite mass  underlies  the  Buck  Creek  region  and  that  the  quartz  porphyry 
dikes  represent  the  final  expulsive  effort  of  this  magma.  After  the 
advent  of  the  porphyry  emanations  carrying  metallic  salts  in  solution 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358  PL.  Ill 


A.  THIN  SECTION  OF  ACTINOLITE-CASSITERITE  ROCK;  CROSSED  NICOLS. 
Magnification  32  diameters.  Shows  cassiterite  transfixed  by  actinolite  needles. 


11.  THIN  SECTION  OF  STANNIFEROUS  METAMORPHOSED  LIMESTONE  FROM  BROOKS 

MOUNTAIN. 

Magnification  12  diameters.  Hulsite  (black  opaque  mineral)  intergrown  with  vesuvianite  in  a matrix  of  calcite. 


ECONOMIC  GEOLOGY. 


85 


ascended  from  unknown  depths.  These  solutions  moved  in  part 
along  preexisting  lines  of  weakness  marked  by  the  quartz  porphyry 
dikes  and  in  part  along  fractures  in  the  slates.  They  contained  the 
elements  silicon,  oxygen,  sulphur,  arsenic,  boron,  iron,  aluminum,  and 
tin,  and  probably  gold.  The  metasomatic  alterations  indicate  that 
the  solutions  were  at  high  temperatures.  The  actinolite  rock  was 
probably  produced  by  stanniferous  solutions  which,  as  leakages  from 
the  main  channels  of  circulation,  moved  laterally  through  impure 
dolomite  beds,  such  as  the  petrographic  study  of  the  slates  has  shown 
to  occur  through  the  region.  The  association  of  cassiterite  and  ar- 
senopyrite  in  a gangue  of  actinolite  is  unique.  Actinolite,  together 
with  axinite  and  other  borosilicates,  however,  occurs  as  a gangue 
material  in  certain  Tasmanian  copper  deposits.®  The  explanation 
advocated  for  these  is  essentially  similar  to  that  given  above. 

CAPE  MOUNTAIN. 

Cape  Mountain  forms  the  promontory  fronting  Bering  Strait  at 
the  westernmost  extremity  of  the  American  Continent.  On  the  east- 
ern flank  of  the  mountain  are  a few  widely  scattered  houses,  which 
form  the  settlement  known  as  “ Tin  City.”  Tin  City  is  110  miles  by 
steamer  route  from  Nome,  with  which  it  is  connected  by  telephone. 

GENERAL  GEOLOGY. 

Granite. — Cape  Mountain  consists  of  a granite  mass,  which  has 
invaded  a series  of  crystalline  limestones  of  Carboniferous  age. 
(See  fig.  5.)  The  limestones  are  lying  nearly  flat,  but  with  a slight 
easterly  dip,  and  extend  eastward  nearly  to  the  mouth  of  Baituk 
Creek,  where  they  are  faulted  against  the  slates  of  the  York  area.  At 
the  cape  the  limestones  dip  in  toward  the  granite.  Locally  along  the 
contact,  as  on  Village  Creek,  the  limestone  is  crumpled  and  turned  up 
at  high  angles — phenomena  ascribable  to  the  dynamic  activity  of  the 
intrusive.  Some  fine-grained  olivine  basalt  dikes,  vesicular  and  in 
part  filled  with  calcite  amygdules,  cut  both  granite  and  limestone. 
They  are  without  doubt  by  far  the  youngest  rocks  of  the  area. 

The  granite  of  Cape  Mountain  is  of  a coarse-grained  gray  type, 
containing  numerous  large  porphyritic  feldspars,  either  iriicrocline  or 
orthoclase,  commonly  an  inch  or  so  in  length.  Quartz,  acid  plagio- 
clase,  and  biotite  comprise  the  remaining  essential  constituents.  The 
quartz  is  prevailingly  smoky.  Along  the  contact  with  the  limestone 
the  feldspars  are  locally  aligned  with  their  longer  axes  parallel. 
More  commonly,  however,  the  granite  is  fine  grained  along  its  margin, 
and  fluorite,  tourmaline,  and  white  mica  appear.  Pegmatite  blebs 

a Weed,  W.  H.,  Copper  mines  of  the  world,  New  York,  1907,  p.  J.71. 


36 


TIN  DEPOSITS  OE  SEWARD  PENINSULA,  ALASKA. 


containing  tourmaline  are  common  in  the  body  of  the  granite.  Dikes 
and  sills  of  granite  or  granite  porphyry  cut  the  surrounding  rocks. 

Detailed  mapping  of  the  contact  between  the  granite  and  limestone 
has  shown  that  the  underground  extension  of  the  granite  surface 
dips  steeply  to  the  east  on  the  east  side  of  Cape  Mountain,  but  that 
on  the  north  side  it  slopes  gently  to  the  north  beneath  the  limestone 
capping.  Erosion  has  left  some  thin  wedgelike  remnants  resting 
upon  the  granite  surface.  (See  fig.  6.)  Some  limestone  masses  were 
broken  off  from  the  roof  which  covered  the  granite  at  the  time  of  its 
intrusion  and  were  partly  submerged  in  the  molten  rock.  An  isolated 


Limestone  with  some  schist  Granite 


Fig.  5. — Geologic  sketch  map  of  Cape  Mountain. 

limestone  patch,  which  had  this  mode  of  origin,  rests  in  the  granite 
near  the  head  of  Lagoon  Creek.  Attention  is  drawn  to  these  foun- 
dered blocks  of  limestone  because  if  any  ore  occurs  along  their  con- 
tacts it  can  have  only  a meager  distribution.  The  dikes  and  sills, 
together  with  the  limestone  masses  torn  off  at  the  time  of  intrusion, 
tend  to  produce  a highly  irregular  contact  surface  between  the  lime- 
stone and  the  granite.  This  fact  is  of  practical  importance  when  the 
development  of  contact  ore  bodies  is  being  considered. 

Contact  phenomena. — The  principal  effect  of  the  intrusion  of  the 
granite  on  the  surrounding  limestone  has  been  to  produce  a coarse 


ECONOMIC  GEOLOGY. 


37 


white  marble,  extending  at  a maximum  200  or  300  feet  from  the  con- 
tact. Proximity  to  the  granite  contact  is  in  many  places  indicated 
by  a peculiar  rough  appearance  of  the  limestone,  due  to  the  develop- 
ment of  small  patches  of  lime-silicate  minerals,  ordinarily  invisible 
to  the  eye.  These  weather  out  in  relief  and  give  it  a characteristic 
“ shaggy  55  appearance  near  the  granite.  At  other  points  delicate 
radial  groups  of  tremolite  appear  on  the  weathered  surfaces  of  sili- 
ceous phases  of  the  limestone.  A faint  banding  is  also  evident,  due 
to  the  fact  that  the  pure  carbonate  laminae  have  been  converted  to 
calc  spar.  The  siliceous  bands  in  the  limestone  overlying  the  granite 
near  the  summit  of  Cape  Mountain  have  been  converted  into  wollas- 
tonite.  At  the  contact  on  Bering  Strait  beds  of  almost  solid  wollas- 
tonite  2 or  3 feet  thick  inclose  an  alaskite  sill  1 foot  thick  and  extend 
30  feet  from  the  main  granite  mass. 

Contact  metamorphism  involving  an  addition  of  material  is  of  rela- 
tively rare  occurrence  and  is  confined  mainly  to  the  limestone  adjoin- 
ing the  dikes  and  sills.  On  the  Canoe  claim  an  open  cut  exposes  a 


0 iooo  2000  feet 

1  i i i 

Fig.  6. — Geologic  section  across  Lagoon  Creek,  Cape  Mountain. 

sill  8 feet  thick,  consisting  of  the  normal  porphyritic  granite  of  Cape 
Mountain.  The  upper  1^  feet,  however,  consist  of  coarse  alaskite- 
pegmatite  composed  of  orthoclase  and  quartz  individuals  4 to  5 
inches  in  length.  Between  the  pegmatite  and  the  porphyritic  gran- 
ite a zone  of  relatively  fine-grained  granite  up  to  6 inches  thick 
intervenes,  but  no  great  regularity  can  be  observed  for  this  feature, 
as  all  three  phases  may  be  confusedly  intermingled.  The  question 
whether  the  pegmatite  did  not  represent  a separate  intrusion  along 
the  contact  was  considered,  but  as  large  quartz  individuals  with  pyra- 
midal terminations  wTere  found  projecting  from  the  pegmatite  into 
the  fine-grained  granite,  and  as  transitions  are  everywhere  observable 
between  the  three  phases,  the  conclusion  was  unavoidable  that  it  was 
practically  contemporaneous  with  the  granite.  Some  tourmaline  is 
of  later  origin  and  is  developed  along  seams.  This  occurrence  re- 
sembles the  “ stockscheider  ” — a peripheral  zone  of  giant  granite  en- 
veloping the  stanniferous  granite  bosses  of  the  Saxon  Erzgebirge — 
and  suggests  Elie  de  Beaumont’s  observation a “ that  the  peculiar 


° Cotta,  B.,  Gangstudien  I,  Freiberg,  1850,  p.  398. 


38  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

cause  of  the  coarsely  crystalline  character  of  the  granite  had  acted 
mainly  upon  the  marginal  portion  of  the  eruptive  mass.”  The  lime- 
stone overlying  the  pegmatite  selvage  is  marmorized,  and  where  in 
immediate  contact  has  been  converted  into  a heavy  green  finely 
granular  rock.  Under  the  microscope  this  proves  to  be  a pyroxene- 
fluorite  hornfels  composed  essentially  of  hedenbergite  and  fluorite, 
with  accessory  calcite  and  quartz.  Scheelite  and  pyrrhotite  occur  in 
a few  scattered  grains.  The  association  of  a pyroxene  hornfels  with 
similar  pegmatitic  selvages  is  repeated  at  various  other  points  on 
Cape  Mountain.  Near  the  Percy  shaft  the  hornfels  consists  of  heden- 
bergite, calcite,  and  scapolite,  with  accessory  scheelite.  The  scheelite 
occurs  in  round,  droplike  grains  embedded  in  calcite  or  intercrystal- 
lized  with  the  pyroxene.  It  resembles  titanite  and  cassiterite,  but 
may  be  distinguished  from  the  former  by  its  positive  uniaxial  char- 
acter and  from  the  latter  by  its  moderate  birefringence  (0.016). 
Inasmuch  as  scheelite  is  not  commonly  recorded  as  a contact-meta- 
morphic  mineral,  the  hornfels  was  submitted  to  E.  C.  Sullivan,  of 
the  United  States  Geological  Survey,  who  verified  chemically  the 
presence  of  tungsten.  The  pannings  from  approximately  10  grams 
of  rock  were  fused  with  Na2C03,  the  fused  mass  was  leached  with 
water,  the  tungsten  was  precipitated  with  HgCl2  as  Hg2W04,  the 
mercury  was  expelled  from  the  tungstate  by  heat,  and  the  residue 
was  examined  by  the  reduction  tests  with  Zn  and  Sn.  The  rock  was 
also  tested  for  chlorine  by  Doctor  Sullivan  and  gave  a strong  reaction 
for  this  element,  thus  confirming  the  optical  determination  of  the 
scapolite. 

ORE  DEPOSITS. 

Cassiterite  probabty  occurs  in  three  ways  at  Cape  Mountain — (1) 
in  tourmalinized  peripheral  portions  of  the  main  granite  mass  and  in 
tourmalinized  granite  dikes;  (2)  in  contact-metamorphic  rock,  and 
(3)  in  veins  in  granite  and  as  an  impregnation  of  the  adjoining  wall 
rocks.  From  experience  in  developed  tin  regions  it  appears  that  the 
first  type  of  occurrence  is  apt  to  be  of  low  grade,  and  that  the  second 
is  an  unlikely  source  of  tin  ore.  The  occurrences  on  Cape  Mountain 
indicate  that  the  Alaskan  deposits  will  prove  to  be  no  exceptions  to 
this  rule.  The  third  is  the  normal  type  the  world  over,  and  has 
yielded  the  deepest  and  most  productive  mines. 

At  Cape  Mountain  no  practical  distinction  is  made  between  the 
first  and  the  second  modes  of  occurrence.  The  largest  amount  of 
prospecting  has  been  done  along  the  granite-limestone  contacts  be- 
cause some  rich  pockets  of  tin  ore  have  been  discovered  in  tourmalin- 
ized granite  along  the  contact  and  because  of  the  distinctive  character 
of  the  contact-metamorphic  rocks  (pyroxene  hornfels).  It  can  not  be 
positively  asserted  that  cassiterite  occurs  in  the  contact-metamorphic 


ECONOMIC  GEOLOGY. 


39 


rock  (in  fact,  all  observations  have  been  to  the  contrary),  but  it  is 
not  improbable  that  some  tin  ore  may  occur  in  the  tourmalinized 
limestone  adjoining  tourmalinized  granite. 

Some  of  the  dikes  cutting  the  limestone  show  margins  which  are 
strongly  tourmalinized  and  considerably  impregnated  with  cassiter- 
ite.  Large  masses  of  bluish  tourmaline  occur,  and  these  carry  rich 
pockets  of  tin  ore  of  a light-brownish  color.  The  limestone  adjoin- 
ing the  dikes  has  here  and  there  been  converted  into  coarse  white 
spar,  in  which  numerous  prisms  and  columns  of  tourmaline  are  em- 
bedded. Where  tourmalinization  has  been  complete  it  may  be  diffi- 
cult to  distinguish  tourmalinized  limestone  from  tourmalinized  dike 
rock.  The  tourmalinization,  either  of  granite  or  limestone,  however, 
appears  to  be  purely  local  and  erratic  in  occurrence.  Furthermore, 
the  tourmaline  rock,  although,  as  already  stated,  locally  rich  in  cas- 
siterite, is  in  general  quite  barren. 

Along  the  periphery  of  the  main  granite  mass  local  tourmaliniza- 
tion of  the  granite  has  taken  place,  accompanied  by  an  introduction 
of  cassiterite  and  pyrite.  The  pyrite  has  largely  been  oxidized,  and 
in  this  way  heavy  red  porous  masses,  consisting  chiefly  of  iron  oxide, 
with  tourmaline  and  cassiterite,  have  been  produced. 

The  contact  rocks  adjoining  the  large  granite  stock  and  some  of  the 
granite  sills  have  been  prospected  at  a number  of  places.  A heavy 
green  rock,  showing  in  places  finely  disseminated  pyrrhotite,  has  been 
regarded  as  tin  ore,  but  microscopic  and  chemical  analysis  fail  to 
reveal  any  tin.  The  green  rock  is  locally  known  both  as  “ greenstone  ” 
and  as  “ tinstone.”  It  is  a finely  granular  rock,  consisting  of  pyrox- 
ene, probably  hedenbergite,  and  fluorite  in  equal  proportions.  This 
rock  is  well  exposed  in  a cut  on  the  Canoe  claim,  where  a few  feet  of 
it  directly  overlies  a granite  sill,  8 feet  thick.  At  other  points  on  Cape 
Mountain,  notably  one-half  mile  north  of  the  Lucky  Queen  property, 
the  pyroxene  is  embedded  in  calcite.  The  pyroxene,  which  is  un- 
usually well  developed  for  a contact-metamorphic  rock,  is  of  brown 
color  and  does  not  look  unlike  cassiterite,  especially  cassiterite  which 
shows  a macroscopic  cleavage.  It  is  true  that  cassiterite  has  a more 
splendent  luster,  but  the  distinction  is  not  one  that  carries  conviction. 
"Where  the  presence  of  tin  is  suspected  in  such  rocks,  only  assays  can 
give  reliable  information. 

The  statements  regarding  deposits  of  contact-metamorphic  origin 
made  for  the  Ear  Mountain  region  are  equally  applicable  to  Cape 
Mountain.  In  addition,  the  highly  irregular  nature  of  the  granite 
contact  makes  prospecting  for  such  deposits  difficult  and  would  entail 
heavy — probably  unwarrantable — expenses  in  mining  them. 

Up  to  the  present  time  a single  narrow  quartz  vein  has  been  found 
in  place,  cutting  the  granite  on  the  north  side  of  Cape  Mountain  at 
an  altitude  of  1,850  feet.  The  vein  is  accompanied  by  some  alteration 


40 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


to  greisen  and  partial  tourmalinization  of  the  adjoining  granite — 
changes  characteristic  of  tin-bearing  veins.  At  other  points  on  Cape 
Mountain  cassiterite,  accompanied  by  tourmaline,  is  found  as  an  im- 
pregnation of  the  granite  adjoining  slips  or  fault  planes.  This  type 
of  occurrence,  in  the  opinion  of  the  writer,  holds  out  greater  possibil- 
ities for  the  future  of  the  district  as  a tin  producer  than  the  other 
two.  Unfortunately,  exploratory  work  has  been  mainly  confined  to 
the  contact  deposits. 

DEVELOPMENTS. 

At  the  time  of  visit  two  properties  only  were  being  actively  pros- 
pected at  Cape  Mountain — those  of  the  United  States  Alaska  Tin 
Mining  Company  and  the  Bartels  Tin  Mining  Company.  The  for- 
mer property  is  situated  near  the  summit  of  the  mountain,  on  the 
north  side.  Developments  up  to  the.  end  of  July,  1907,  consisted  of  a 
shaft  reported  to  be  22  feet  deep,  now  filled  with  water,  and  a 7-foot 
tunnel,  270  feet  long.  The  company  has  also  erected  a 10-stamp 
mill  near  the  beach  at  Tin  City.  Four  men  were  employed  at  the 
time  of  visit.  The  shaft  is  sunk  on  a quartz  ledge,  1 foot  thick, 
striking  N.  45°  W.  (magnetic)  and  dipping  80°  E.  The  tunnel, 
whose  altitude  at  the  portal  is  1,G00  feet,  according  to  aneroid  meas- 
urement, is  driven  in  a direction  S.  40°  W.  through  hard,  firm  gran- 
ite, and  is  expected  to  tap  the  ledge  250  feet  below  the  collar  of  the 
shaft. 

The  principal  development  work  by  the  Bartels  Tin  Mining  Com- 
pany has  been  done  on  the  North  Star  property.  Eight  men  were 
employed  during  the  summer  of  1907.  The  main  tunnel,  with  its 
drifts  and  winzes,  aggregated  750  feet  in  length.  This  tunnel  is 
being  driven  to  catch  the  granite-limestone  contact  at  a depth  of  100 
feet  below  the  workings  of  the  Lucky  Queen  tunnel.  About  400  feet 
from  the  mouth  of  the  tunnel  a band  of  granite,  carrying  numerous 
visible  crystals  of  cassiterite,  associated  with  some  tourmaline,  was 
encountered.  The  width  of  this  band  is  about  18  inches.  The  granite 
is  soft  and  iron  stained.  The  succeeding  8 feet  consists  of  hard  gray 
granite  with  pyrite  disseminated  through  it.  This  is  succeeded  by 
15  feet  of  iron-stained  granite.  At  the  time  of  visit  the  18-inch  belt 
of  rich  tin  ore  had  not  been  drifted  on  to  prove  its  persistence.  The 
drifts  branching  off  from  the  main  adit  follow  the  contact  of  a large 
limestone  block,  which  was  evidently  torn  from  the  main  limestone 
mass  during  the  intrusion  of  the  granite.  In  following  this  contact, 
which  proved  to  be  of  a highly  irregular  nature,  several  winzes  were 
necessary.  A new  tunnel,  67  feet  below  the  North  Star  tunnel,  is 
being  run  from  the  surface  to  connect  with  the  lowest  drifts  reached 
by  these  winzes.  The  granite  along  the  limestone  contact  is  charged 
with  numerous  radiating  groups  of  tourmaline  prisms  associated 


ECONOMIC  GEOLOGY. 


41 


with  iron  oxide,  and  locally  with  pyrite  and  tin  ore.  Crushing  and 
oxidation  have  taken  place  along  the  contact,  and  heavily  iron 
stained  gouge  matter,  a foot  in  thickness,  has  been  produced.  At 
points  where  the  red  clayey  material  is  absent  the  granite  is  fresh 
and  the  progressive  increase  of  fineness  of  grain  as  the  contact  is 
approached  can  be  noted. 

A considerable  portion  of  the  energies  of  the  company  has  been 
expended  on  assessment  work  on  the  numerous  claims  which  it  holds 
on  Cape  Mountain. 

On  the  Carlson  & Goodwin  property  an  adit  20  feet  long  has  been 
driven  along  the  contact  of  a horizontal  limestone  and  a granitic 
dike.  The  dike  sends  small,  irregular  tongues  into  the  limestone, 
and  the  ends  of  these  tongues  have  been  completely  converted  into 
blue  tourmaline  rock.  The  limestone  has  been  rendered  coarsely 
crystalline,  but  evinces  no  other  change.  Bock  from  the  dump,  how- 
ever, shows  that  locally  an  intense  tourmalinization  was  produced. 
No  stanniferous  rock  was  seen  in  place. 

On  the  northwest  side  of  the  mountain,  on  Village  Creek,  some 
drill  holes  have  been  put  down  to  the  granite  contact,  but  the  results 
are  not  known. 

BROOKS  MOUNTAIN. 

Brooks  Mountain,  the  dominant  peak  of  the  York  Mountains,  lies 
in  the  watershed  of  the  Bering  and  Arctic  drainages.  It  is  easily 
accessible  from  the  coast  by  way  of  Lost  Biver,  a distance  of  9 miles. 
The  mineral  deposits  are  of  contact-metamorphic  origin,  and  though 
no  cassiterite-bearing  rock  has  been  discovered  on  the  mountain,  yet 
the  character  of  the  mineralization  here  allies  it  to  that  of  the  tin 
region,  of  which  Brooks  Mountain  is  geographically  a part. 

An  intrusive  granite  mass,  2 miles  long  by  two-thirds  of  a mile 
vide,  forms  the  southern  flank  of  the  mountain.  The  granite  is 
characterized  by  the  presence  of  numerous  large  porphvritic  ortho- 
clase  crystals,  commonly  an  inch  in  diameter,  and  large  idiomorphic 
crystals  of  smoky  quartz  exceeding  peas  in  size.  The  matrix  con- 
sists of  a coarsely  granular  assemblage  of  orthoclase  and  subordinate 
oligoclase  (Ab80An20),  with  quartz  and  biotite  in  small  amounts. 
The  rocks  surrounding  the  granite  are  chiefly  limestones  of  the  Port 
Clarence  formation,  and  are  highly  crumpled  throughout  much  of 
the  region.  Along  the  periphery  of  the  granite  they  have  been  mar- 
morized,  and  an  extensive  variety  of  contact-metamorphic  minerals 
have  been  produced  in  the  immediate  vicinity  of  the  contact. 

At  the  west  end  of  the  granite  stock  a horizontal  pegmatite  about 
8 inches  thick  traverses  the  white  marble.  It  consists  of  orthoclase, 
quartz,  and  biotite,  generally  segregated  in  separate  masses,  the  bio- 
tite in  plates  one-half  inch  in  diameter  forming  selvages  1 to  2 inches 


42 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


thick.  Thin  sections  cut  from  equidimensional  portions  of  the  peg- 
matite show,  in  addition  to  the  three  constituents  already  named,  a 
small  amount  of  plagioclase,  some  faint-colored  bluish-green  mica, 
accessory  corundum,  and  probably  topaz.  The  structure  is  allotrio- 
morphic  granular.  The  pegmatite  "is  overlain  by  1 foot  of  finely 
granular,  heavy  green  rock,  resembling  that  adjoining  the  pegmatite 
selvages  on  Cape  Mountain.  This  rock  is  composed  of  vesuvianite, 
hedenbergite,  and  fluorite  in  approximately  equal  proportions. 

Vesuvianite  is  the  commonest  mineral  in  the  metamorphic  aureole 
of  the  granite  mass.  Along  the  headwaters  of  Yankee  Creek  the  im- 
pure crumpled  Port  Clarence  limestone  is  brought  into  contact  with 
the  intrusive  stock,  and  a thorough  recrystallization  has  ensued. 
Crystallographically  perfect  vesuvianite  in  prisms  up  to  three- fourths 
inch  in  length  occurs  scattered  in  great  profusion  through  a matrix 
of  coarse  white  calc  spar.  The  vesuvianite  is  noteworthy  as  contain- 
ing 0.88  per  cent  B203.a  Where  this  mineral  has  not  individualized 
into  large  crystals  the  metamorphosed  rock  consists  of  a fine  equi- 
granular  aggregate  of  vesuvianite,  calcite,  and  possibly  garnet,  inter- 
spersed with  minute  plates  of  phlogopite.  The  growth  of  the  large 
crystals  has  produced  a clarification,  as  it  were,  of  the  carbonate  rock, 
and  the  boron  content  of  the  vesuvianite  shows  that  this  process  was 
promoted  by  pneumatolytic  agents.  In  this  connection  it  is  signifi- 
cant that  an  energetic  tourmalinization  of  the  granite  has  taken  place 
at  a number  of  points  in  the  vicinity  of  this  portion  of  the  contact. 

At  the  west  end  of  the  Brooks  Mountain  granite  mass  a prospect 
trench  discloses  a body  of  argentiferous  galena  ore,  occurring  20  feet 
from  the  granite  contact  in  a coarsely  crystalline  white  limestone. 
The  strike  of  the  ore  body,  as  revealed  in  the  open  cut,  is  N.  15°  W. 
(magnetic),  and  the  dip  65°  toward  the  granite.  A thickness  of 
8^  feet  of  solid  ore  is  exposed,  consisting  of  galena  strongly  admixed 
with  a lustrous  black  zinc  blende  which,  as  analysis  shows,  contains 
19  per  cent  of  ferrous  iron.  Some  pyrrhotite  is  also  present,  but  this 
mineral  is  comparatively  rare.  Where  any  gangue  mineral  is  visible 
it  consists  of  fluorite.  The  ore  body  is  frozen  to  both  walls.  The 
hanging  wall  shows  a belt  of  finely  granular  fluorite  several  inches 
thick,  succeeded  by  extremely  coarse  calcite  containing  scattered  crys- 
tals of  diopside  and  some  galena.  The  grain  of  the  calcite  decreases 
away  from  the  ore  body.  A thin  section  of  rock  taken  from  a point 
near  the  hanging  wall  is  composed  of  calcite,  fluorite,  diopside,  calcic 
plagioclase  (Ab2An3),  an  unknown  positive  uniaxial  mineral,  and  a 
small  amount  of  colorless  mica,  with  sporadic  grains  of  the  ore  min- 
erals. Assays  of  the  ore  made  in  Nome  yielded  34  per  cent  of  lead 

° This  determination  was  made  by  I'rof.  Edgar  F.  Smith,  of  the  University  of  Penn- 
sylvania, according  to  two  new  methods  for  the  estimation  of  B203  that  he  has  recently 
discovered. 


ECONOMIC  GEOLOGY. 


43 


and  11  ounces  of  silver  per  ton.  Other  assays  were  reported  to  give 
ore  values  ranging  from  $17  to  $44  per  ton. 

In  the  vicinity  of  the.  galena  prospect  there  is  some  contact-meta- 
morphosed limestone  containing  a fibrous  green  magnesia-iron  boron 
mineral  (ludwigite?)  intercrystallized  with  galena.  Loose  masses  of 
paigeite  hornfels  are  also  present.  Some  rock  containing  abundant 
honey-yellow  crystals  of  chondrodite  and  numerous  minute  octaliedra 
of  spinel,  embedded  in  a mesostasis  of  calcite  with  accessory  magnet- 
ite, occurs  near  by. 

In  the  same  general  locality  some  contact  masses  of  vesuvianite 
have  been  prospected  for  nickel.  The  vesuvianite  is  in  part  finely 
granular  and  gives  the  rock  a general  green  color.  This  feature  and 
the  unusual  weight  of  the  rock  (that  is,  compared  to  quartz)  doubt- 
less caused  the  nickel  prospecting.  No  indications  of  nickel  are  pres- 
ent, and  it  may  be  added  that  such  a mode  of  occurrence  is  totally 
unknown  for  nickel.  On  microscopic  examination  small  amounts  of 
calcite,  deeply  pleochroic  biotite,  and  hedenbergite  are  found  asso- 
ciated with  the  vesuvianite. 

In  the  canyon  below  the  galena  claim  some  assessment  work  has 
been  done  on  a showing  of  contact-metamorphic  minerals  near  the 
granite  contact.  The  deposit  is  interesting  from  a scientific  stand- 
point, inasmuch  as  a hitherto  unknown  boron-tin  mineral  has  been 
discovered  in  it,  but  nothing  of  great  commercial  importance  has  been 
found  here.  The  minerals  comprise  brown  garnet,  showing  rhombic 
faces,  green  or  yellowish-green  vesuvianite,  and  abundant  magnetite 
closely  associated  with  the  new  mineral — a magnesia-iron  tin  borate 
which  has  been  named  hulsite.®  These  various  minerals  are  all  in- 
cluded in  a matrix  of  coarse  white  spar  (PI.  Ill,  B).  On  account  of 
the  low  percentage  of  tin  in  hulsite  (approximately  10  per  cent)  the 
deposit  can  have  no  economic  value. 

At  the  head  of  the  same  canyon  other  contact-metamorphic  deposits 
have  received  attention.  Here,  at  an  altitude  of  2,000  feet,  a small 
prospect  hole  exposed  a mass  of  metamorphic  minerals  occurring  in 
a white  marble  a few  feet  from  the  granite  contact.  Tourmaline, 
fluorite,  calcite,  arsenopyrite,  brilliant  black  sphalerite,  pyroxene,  and 
axinite  occur  confusedly  intergrown.  The  ore  body  is  4 feet  thick  and 
penetrates  the  marmorized  limestone  in  irregular  tongues  a few  inches 
thick.  Some  galena  was  noted  in  the  ends  of  these  tongues,  which 
were  examined  microscopically  and  found  to  consist  almost  exclu- 
sively of  monoclinic  pyroxene.  A few  hundred  feet  north  of  this  oc- 
currence the  pure  Avhite  marble  gives  way  to  a highly  metamorphosed 
impure  limestone,  consisting  essentially  of  vesuvianite,  calcite,  bio- 
tite, and  accessory  tourmaline.  Some  of  this  rock  contains  sphalerite 


“Am.  Jour.  Sci.,  4th  ser.,  vol.  25,  1908,  p.  323. 


44  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

and  other  sulphurets,  which  on  oxidizing  give  it  a gossan  appearance. 
High  gold  assays  were  claimed  from  this  type  of  rock.  Ledoux  & Co., 
of  New  York,  report  on  an  assay  sample  submitted  by  the  Survey: 
“ Gold,  trace ; silver,  0.23  ounce.” 

On  the  north  side  of  Brooks  Mountain,  at  an  altitude  of  1,850  feet, 
is  a small  galena  prospect.  The  galena  occurs  in  a gossan,  the  skeleton 
of  which  consists  of  tourmaline.  The  iron  oxide  of  the  gossan  con- 
tains lead  and  traces  of  bismuth,  the  lead  probably  as  carbonate  and 
the  bismuth  as  oxide. 

LOST  RIVER. 

LOCATION. 

Lost  River  is  a small  stream  rising  in  the  heart  of  the  York  Moun- 
tains in  the  western  part  of  Seward  Peninsula.  It  flows  southward 
into  Bering  Sea  through  a comparatively  broad  and  open  valley, 
except  for  a short  stretch  near  its  mouth,  where  it  flows  in  a narrow 
canyon.  It  has  a total  length  of  9 miles.  The  region  is  nearly  desti- 
tute of  vegetation,  even  Arctic  mosses  being  scarce.  The  tin  prospects 
are  on  Cassiterite  Creek  (see  fig.  7),  a branch  of  Lost  River,  6 miles 
from  the  coast,  and  are  easily  accessible  by  a good  wagon  roadway. 
A tungsten-silver  prospect,  a copper  prospect,  and  some  galena 
prospects  are  also  situated  in  this  region. 

GENERAL  GEOLOGY. 

The  rocks. — The  general  geologic  features  of  the  region  are  simple. 
The  bed  rock  consists  of  the  Port  Clarence  limestone,  dipping  north- 
ward at  an  angle  of  20°.  Near  the  head  of  Cassiterite  Creek  the 
limestone  is  intimately  banded  with  argillaceous  laminae,  and  in- 
tensely crumpled  (PI.  II,  B ).  Locally  the  formation  is  fractured 
and  brecciated,  and  shear  zones  of  white  marble  have  been  formed. 

On  Tin  Creek,  another  tributary  of  Lost  River,  a small  granite 
boss,  a third  of  a mile  in  diameter,  is  intruded  into  the  limestone. 
The  granite  is  a medium-grained  aggregate  of  feldspar,  quartz 
(which  is  partly  idiom orphic,  smoky,  and  conspicuous),  and  scat- 
tered foils  of  biotite.  The  principal  effect  of  this  intrusion  has  been 
to  marmorize  the  surrounding  limestone,  though  locally  some  large 
masses  of  contact-metamorphic  minerals  have  been  formed. 

A considerable  number  of  vertical  quartz  porphyry  dikes  pierce 
the  limestone,  but  only  one  has  been  found  extending  into  the  granite 
area.  They  are  fairly  persistent,  and  can  be  traced  for  several  miles 
across  the  country.  They  are  not  all  strictly  contemporaneous  in- 
trusions, as  certain  dikes  have  been  found  to  intersect  each  other. 
The  quartz  porphyries  are  light-colored  rocks  containing  small  glassy 
quartz  and  feldspar  crystals  embedded  in  an  aphanitic  matrix.  The 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358'  PL.  IV 


D 

A.  ORBULE  PRODUCED  BY  CONTACT  METAMORPHISM. 

B.  REVERSE  SIDE  OF  ORBULE  SHOWN  IN  A. 

C.  MAXIMUM  ORBULE;  DIAMETER,  8 INCHES. 

D.  IRREGULAR  ORBULES. 


ECONOMIC  GEOLOGY. 


45 


main  tin  prospects  of  the  region  occur  in  a few  highly  altered  dikes 
of  this  character,  but  several  of  the  other  dikes  have  received  sepa- 
rate names  and  have  been  more  or  less  prospected,  on  what  encour- 
agement, however,  it  is  difficult  to  understand.  They  are  usually 
unmineralized,  except  for  sporadic  cubes  of  pyrite,  and  there  is 
no  known  reason  why  they  should  become  tin  bearing  in  depth. 


Fig.  7. — Geologic  sketch  map  of  Cassiterite  Creek  and  vicinity.  Topography  by  Adolph 
Knopf.  Elevations  determined  by  aneroid  barometer. 

Orbicular  contact  metamorphism. — The  limestone  surrounding  the 
granite  boss  of  Tin  Creek  has  been  converted  into  a coarse  white 
marble.  Near  the  contact  loose  blocks  showing  orbicular  forms  are 
common  (Pis.  IV,  V,  VI,  B).  The  orbules  are  composed  of  an  alter- 
nating succession  of  concentric  black  and  white  bands,  commonly  a 


46 


TIN  DEPOSITS  OF  SEWAED  PENINSULA,  ALASKA, 


millimeter  or  so  in  breadth.  As  shown  in  the  photographs,  the 
orbicular  structure  is  brought  out  in  detail  by  the  etching  action  of 
the  weather.  Many  of  the  sections  through  the  orbules  are  perfect 
circles,  a maximum  diameter  of  8 inches  being  noted,  but  elliptical 
forms,  due  to  the  interference  of  contiguous  orbules,  are  common. 
In  some  places  small  orbules  occur  m the  outer  bands  of  large  orbules 
and  cause  a wrinkling  of  the  even  banding.  Where  several  small 
independent  orbules  have  formed  around  closely  spaced  centers  highly 
intricate  structure  resembling  that  of  contorted  gneiss  has  been 
evolved. 

The  minerals  composing  the  orbules,  named  in  their  order  of  abun- 
dance, are  fluorite,  hornblende,  vesuvianite,  plagioclase  (Ab3An7), 
and  magnetite.  The  hornblende  is  a deep-colored  variety,  the 
pleochroism  ranging  from  brown  to  strong  greenish  blue.  The 
vesuvianite  has  a tendency  to  form  radial  groups  of  short,  stout 
columns.  Under  the  microscope  the  banded  structure  is  not  as  dis- 
tinctly apparent  as  would  be  expected  from  inspection  of  the 
weathered  surface  of  the  orbules.  The  light-colored  bands  consist 
of  mutual  intergrowths  of  fluorite  and  plagioclase;  the  dark  bands 
consist  of  fluorite  with  hornblende  or  vesuvianite,  or  with  both 
together,  and  commonly  some  magnetite.  The  presence  of  fluorite 
in  both  dark  and  light  colored  bands  causes  them  to  contrast  less 
emphatically  under  the  microscope  than  they  do  macroscopically. 
Examined  in  thin  section  the  central  portion  of  one  of  the  orbules  was 
found  to  consist  of  calcite  anhedra  in  which  are  embedded  vesu- 
vianite, fluorite,  and  green  amphibole  inclosing  considerable  magnet- 
ite. This  central  area  is  surrounded  by  a ring  of  magnetite.  Other 
centers  are  composed  chiefly  of  fluorite  and  vesuvianite  with  inter- 
grown  hornblende.  An  unusual  type  of  orbule  is  one  composed  of 
garnet,  pyroxene,  and  fluorite,  with  narrow  black  bands  of  magnetite. 

A single  exposure  outcropping  beneath  the  talus  near  the  granite- 
limestone  contact  throws  light  on  the  genesis  of  these  remarkable 
forms.  Curious  veins,  symmetrically  banded,  traverse  the  marmor- 
ized  limestone  in  irregular  fashion.  The  bands  are  only  a fraction 
of  a millimeter  in  thickness  and  simulate  the  sinuous  flow  lines  of 
certain  acidic  volcanic  rocks  (PI.  V).  Small  tongues,  a few  inches 
in  length,  project  into  the  marble,  and  these  also  are  symmetrically 
banded.  In  irregular  expansions  of  the  veins  orbicular  structures 
have  been  developed  (PL  VI,  B ).  The  veins  are  composed  of  fluorite 
and  calcic  plagioclase  (Ab1An2),  with  pyroxene,  green  mica,  horn- 
blende, and  accessory  arsenopyrite,  cassiterite,  and  scheelite.  They 
therefore  resemble  the  orbules  in  miner alogical  constitution  to  a 
considerable  extent. 

The  orbicular  material  is  cut  by  quartz  porphyry,  thus  fixing  the 
period  of  its  formation,  although  not  very  closely.  The  only  quartz 
porphyry  dike  penetrating  the  granite  shows  strong  marginal  chill- 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358  PL.  V 


BANDED  VEIN;  A SUPPLY  DUCT  FOR  THE  ORBULES. 


Natural  size. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358  PL.  VI 


A.  BANDED  APOPHYSIS  FROM  GARNET-VESUVIANITE  MASS  ON  TIN  CREEK. 
Natural  size. 


B.  ORBULES  IN  MARBLE  MATRIX,  SHOWING  MODE  OF  ORIGIN. 


ECONOMIC  GEOLOGY. 


47 


ing,  indicating,  therefore,  a considerable  interval  between  the  intru- 
sion of  the  granite  and  the  injection  of  the  dikes.  How  nearly  con- 
temporaneous were  the  solidification  of  the  granite  and  the  meta- 
morphism is  an  open  question. 

A mass  of  metamorphic  minerals  50  feet  wide  is  exposed  on  the 
bank  of  Tin  Creek,  1,000  feet  from  the  visible  contact  of  the  granite 
and  limestone.  It  consists  of  solid  masses  of  radial  anci  arborescent 
vesuvianite  and  of  brown  garnet  showing  dodecahedral  faces.  The 
microscope  reveals  in  addition  small  amounts  of  interstitial  fluorite 
and  calcite  and  accessory  pyroxene,  hornblende,  and  plagioclase. 
The  dark  mass  of  metamorphic  minerals  has  injected  apophyses,  as  it 
were,  into  the  adjoining  limestone  (PI.  VI,  A).  These  are  arranged 
in  black  and  white  bands,  a fraction  of  a millimeter  in  thick- 
ness. The  microscope  shows  that  these  apophysal  veins  are  com- 
posed of  fluorite,  strongly  pleochroic  from  brown-green  to  blue-green 
hornblende,  vesuvianite,  and  calcite,  with  accessory  magnetite  and 
arsenopyrite.  These  features  ally  this  occurrence  with  the  orbicular 
contact  metamorphism  and  suggest  that  the  heavy  vesuvianite-garnet 
masses  were  produced  by  magmatic  solutions  traveling  outward  along 
fissures  in  the  limestone. 

Forms  similar  to  the  orbicular  structures  have  not  previously  been 
recorded.  Triistedt  a has  recently  described  some  curious  occurrences 
(“  Erzschlauche,”  he  terms  them)  from  Pitkaranta,  in  Finland, 
which  in  their  essential  aspects  resemble  the  banded  veins  serving  as 
the  supply  ducts  for  the  Alaskan  orbules.  Cross  sections  of  the  ore 
arteries  resemble  sections  through  the  orbules  and,  moreover,  show  a 
similarity  in  mineralogical  constitution  and  similar  alternating  bands 
composed  of  magnetite  and  fluorite-vesuvianite  with  sporadic  garnet. 
The  explanation  advanced  for  the  ore  arteries,  which  anastomose 
through  a limestone,  is  that  they  are  crustification  structures  produced 
by  juvenile  waters  subject  to  rapid  changes  in  composition  and  tem- 
perature. The  circular  pipes  along  which  the  deposition  took  place 
were  produced  by  the  corrosive  action  of  earlier  solutions.  This 
hypothesis  does  not  fit  the  Lost  River  phenomena.  The  mode  of 
growth  of  the  orbules — outward  from  centers — their  common  inter- 
ferences, and  their  position  adjoining  the  banded  veins  preclude  an 
origin  by  crustification.  Their  essential  similarity  to  the  banded 
veins  and  their  parasitic  habit  show  that  the  two  features  are  identical 
phenomena,  which,  as  already  indicated,  are  allied  to  the  formation  of 
the  vesuvianite-garnet  masses.  The  explanation  which  the  writer 
would  suggest  for  this  related  set  of  phenomena  is  that  it  was  pro- 
duced by  magmatic  emissions  traveling  outward  under  great  pressure 
along  fissures  in  the  limestone ; that  the  flow  of  the  solutions  was  im- 

a Triistedt,  O.,  Die  Erzlagerstiitten  von  Pitkaranta  am  Ladoga-See  : Bull.  Comm.  Geol. 
de  Finlande,  No.  19,  1907,  p.  226. 


48 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


peded ; that  at  points  of  stagnation  the  Avail  rock  was  thoroughly  per- 
meated and  a local  intense  metasomatism  was  produced.  The  solutions 
contained  large  amounts  of  fluorine,  aluminum,  silicon,  iron,  and 
sodium.  The  formation  of  fluorite  (CaF2)  caused  the  expulsion  of  an 
equivalent  quantity  of  C02  from  the  limestone  and,  owing  to  the  ab- 
sorption of  this  gas,  the  capacity  of  the  solutions  to  dissolve  lime  was 
increased  to  a high  degree. 

It  is  probable  that  the  channels  of  circulation  wTere  enlarged  by  this 
process  and  that  the  A^ein  filling  as  now  seen  consists  of  minerals 
formed  from  the  lime  of  the  Avail  rock  and  fluorine,  aluminum,  silicon, 
iron,  and  sodium  derived  from  the  magmatic  solutions.  In  such  veins 
formed  in  limestone  under  conditions  of  high  pressure  and  tempera- 
ture it  appears  to  be  impossible  to  discriminate  between  metasomati- 
cally  altered  wall  rock  and  the  filling  of  the  original  channels  of  circu- 
lation. The  banding  was  produced  either  by  processes  similar  to  those 
which  have  given  certain  igneous  dikes  their  banded  character  or  by 
phenomena  similar  to  those  operatAe  in  the  formation  of  Liesegang’s 
rings.  If  a drop  of  AgNOs  solution  be  placed  upon  a gelatin  plate 
impregnated  Avith  K2Cr207  a series  of  concentric  rings  consisting  of 
Ag2Cr207  will  be  formed,  becoming  progressively  Avider  spaced  with 
increasing  distance  from  the  center.  The  explanation  given  by  Ost- 
Avald  a is  that  as  the  soluble  silver  salt  diffuses  outAvard  a periodic 
precipitation  of  insoluble  silver  chromate  will  take  place  at  the  loci 
of  supersaturation.  Morse  and  Pierce  6 have  investigated  this  phe- 
nomenon in  some  detail,  using  tubes,  howeA7er,  instead  of  plates,  and 
have  shown  incidentally  that  gelatin  is  not  essential  to  the  production 
of  the  rings  and  bands.  Among  other  substances  employed  were 
FeClg  and  Na2C03,  and  a recurrent  evolution  of  C02  was  noted. 
This  reaction  proceeds  as  follows: 

2FeCl3+3H20+3Na2C03=3C02+6NaCl+2Fe(0H)3. 

When  the  attempt  is  made  to  fit  this  explanation  to  the  natural 
conditions  the  problem  becomes  greatly  complicated  on  account  of 
the  complex  character  of  the  solutions,  the  unknoAvn  state  of  combi- 
nation of  the  \7arious  elements,  and  their  different  rates  of  diffusion. 
As  abundant  fluorine  was  present  in  the  solutions,  a reaction  analo- 
gous to  the  preceding  may  be  formulated  as  follows : 

2FeF3+3H20+3CaC03=3C02+3CaF2+2Fe  (OH)  3. 

The  fluorine  Avas  thus  fixed  as  fluorite  and  the  iron  separated  as 
magnetite  or  was  taken  up  by  the  production  of  amphibole.  Enough 


a Lehbruch  allegemeinen  Cliemie,  2d.,  Band  2,  Toil  2,  p.  778. 
b Zeitschr.  physikal.  Cliemie,  vol.  45,  1903,  p.  589. 


ECONOMIC  GEOLOGY. 


49 


has  been  indicated  to  show  that  an  explanation  involving  diffusion 
and  supersaturation  is  at  least  as  plausible  as  one  involving  crusti- 
fication  and  is  in  closer  harmony  with  the  phenomena  observed  in  the 
field. 

CASSITERITE  PROSPECTS. 

Lodes. — At  Tin  Creek  a few  thin  quartz  stringers  carrying  cassit- 
erite  have  been  found  in  the  granite.  Collier  a has  shown  that  some 
pyritiferous  granite  from  the  same  locality  contains  0.3  per  cent  of 
tin.  No  cassiterite  is  visible  in  this  granite  to  the  unaided  eye,  so  on 
account  of  the  prevalence  of  sulphides  he  assumed  that  the  tin  occurs 
in  the  form  of  tin  pyrites  (stannite).  A cut  has  been  opened  on  this 
occurrence  and  shows  a number  of  narrow  bands  of  hard  quartzose 
granite  containing  finely  disseminated  pyrites,  chiefly  of  iron  and 
arsenic.  Under  the  microscope  the  rock  is  seen  to  be  composed  of 
quartz,  topaz,  and  sericitized  feldspar,  with  accessory  pyrite,  arseno- 
pyrite,  and  cassiterite  in  small  amount. 

The  principal  tin  prospects  of  the  region  are  located  on  Cassiterite 
Creek,  and  occur  in  the  quartz  porphyry  dike  known  as  the  Cassit- 
erite lode.  This  dike  is  6 to  10  feet  thick  and  can  be  traced  from 
the  head  of  Tin  Creek  in  a northwesterly  direction  to  Lost  River,  a 
distance  of  9,000  feet.  Near  Lost  River  the  dike  rock  contains  a mul- 
titude of  angular  limestone  fragments  and  is  really  a limestone 
breccia  cemented  by  quartz  porphyry.  The  characteristic  feature  of 
the  Cassiterite  lode  dike  rock,  where  nonstanniferous,  is  the  abun- 
dance of  sharply  defined  quartz  phenocrysts  embedded  in  a white 
aphanitic  matrix.  Thin  sections  cut  from  the  least-altered  portions 
of  the  dike  show  numerous  phenocrysts  of  quartz,  orthoclase,  and 
sodic  plagioclase  embedded  in  a cryptocrystalline  groundmass.  The 
nonlamellated  feldspar  is  opaque  from  kaolinization,  but  the  plagi- 
oclase is  unaltered.  Sporadic  crystals  of  clear  and  limpid  plagioclase 
lie  inclosed  in  turbid  orthoclase  phenocrysts.  Fluorite  is  common 
in  the  groundmass  and  patches  of  topaz  occur  also.  More  highly 
altered  phases  of  the  dike  merely  show  quartz  phenocrysts  lying 
scattered  in  a matrix  of  scaly  white  mica,  fluorite,  and  quartz.  Along 
a portion  of  its  course  the  white  quartz  porphyry  dike  has  broken 
through  an  older  dike,  a gray  feldspar  porphyry,  which  is  particu- 
larly conspicuous  on  account  of  the  multitude  of  dull  white  pheno- 
crysts that  it  contains. 

The  tin-bearing  portion  of  the  dike  is  3,000  feet  long,  but  the  whole 
of  this  length  can  not  be  considered  ore  rock;  intermittent  barren 
stretches  occur,  and  the  ore  is  probably  localized  in  irregular  shoots. 
The  limestone  in  the  vicinity  of  the  stanniferous  portion  of  the  dike 

a Collier,  A.  J.,  Tin  deposits  of  the  York  region,  Alaska  : Bull.  U.  S.  Geol.  Survey  No.  229, 
1904,  p.  22. 

54356— Bull.  35S— 08 4 


50 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


is  seamed  with  innumerable  veinlets  which  reticulate  the  surface  of 
the  country  rock  in  every  conceivable  direction  (Pl.  VII,  A). 
These  vary  in  thickness  from  a film’s  breadth  to  several  inches.  An 
energetic  metasomatic  alteration  has  accompanied  the  veinlets,  and 
cassiterite  is  locally  observed  in  them,  but  nothing  in  the  nature  of  a 
stanniferous  stockwork  has  been  formed. 

The  tin  ore  found  in  the  quartz  porphyry  dike  is  associated  with 
irregular  seams  and  stringers  of  quartz  and  lithia  mica.  Cassiterite 
occurs  both  in  the  stringers  and  as  an  impregnation  of  the  altered 
dike  adjoining  the  stringers.  Where  the  veinlets  are  absent  the 
quartz  porphyry  contains  no  cassiterite,  and  is  hard  and  barren. 
Wolframite  is  commonly  associated  with  the  cassiterite  and,  though 
no  actual  tests  have  been  made,  it  is  probable  that  the  tungsten  con- 
tent of  the  lode  is  as  valuable  as  the  tin.  Pyrite  and  arsenopyrite 
accompany  the  tin  ore  and  more  rarely  sphalerite  and  galena  are 
found.  Locally  the  dike  rock  contains  some  molybdenite.  The  com- 
monest gangue  mineral  is  fluorite,  with  zinnwaldite  next  in  order  of 
abundance.  Thin  sections  show  also  the  presence  of  topaz  in  radial 
aggregates.  Where  alteration  has  been  most  intense  large  drusy 
masses  of  cubical  fluorite  and  mica  occur,  and  from  such  localities 
magnificent  specimens  of  cassiterite  in  black  splendent  crystals  have 
been  obtained.  The  usual  type  of  ore,  however,  is  a soft  kaolinized 
porphyry,  stained  red  with  iron  oxide,  and  impregnated  with  cassit- 
erite, wolframite,  and  sulphides.  The  dike  is  intensely  and  irregu- 
larly slickensided  and  clay  gouge  is  common.  The  limestone  wall 
rock,  however,  is  firm  and  hard.  It  is  considerably  impregnated  with 
fluorite,  which  glows  with  a greenish  light  when  struck  with  the  pick. 
Thin  sections  of  wall  rock  immediately  adjacent  to  the  dike  show  that 
it  consists  of  fluorite  and  radial  topaz,  with  some  colorless  mica. 
Cassiterite  occurs  to  a small  extent  in  the  wall  rock  in  narrow  vein- 
lets  (1  inch  thick)  consisting  of  divergent  columnar  topaz.  In  the 
vicinity  of  these  veinlets  the  fiuoritized  limestone  contains  patches  of 
coarse  fluorspar  and  rosettes  of  topaz. 

A few  hundred  feet  north  of  the  Cassiterite  lode  is  another  quartz 
porphyry  dike,  known  as  the  Ida  Bell  lode.  It  is  about  35  feet 
thick  on  the  summit  of  the  hill  between  Lost  River  and  Cassiterite 
Creek.  The  rock  is  dense  and  fine  grained.  In  the  vicinity  of  Cassit- 
erite Creek  quartz  stringers  an  inch  or  so  in  thickness,  carrying  cas- 
siterite with  some  wolframite,  cut  the  dike,  but  along  its  eastern 
extension  only  sporadic  cubes  of  pyrite  can  be  seen.  The  alteration 
that  is  so  characteristic  a feature  of  the  Cassiterite  lode  is  conspicu- 
ously absent  from  the  Ida  Bell  quartz  porphyry  dike.  The  petro- 
graphic similarity  which  a number  of  other  quartz  porphyry  dikes  in 
the  Lost  River  basin  bear  to  this  dike  has  occasioned  considerable 
useless  prospecting. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358  PL.  VII 


B.  SURFACE  EXPOSURE  SHOWING  OCCURRENCE  OF  FLUORITE-SILICATE  ROCK  ADJOINING 
VEINLETS  IN  LIMESTONE. 


ECONOMIC  GEOLOGY. 


51 


One  mile  north  of  the  Cassiterite  lode  is  another  tin-bearing 
porphyry  dike  named  the  Dolcoath  lode.  It  is  from  2J  to  3 feet 
thick,  strikes  N.  50°  E.  (magnetic)  and  dips  65°  NW.  This  dike 
differs  from  the  two  previously  described  both  in  its  mineralogy  and 
in  the  mode  of  occurrence  of  the  tin  ore.  It  is  so  highly  altered  and 
mineralized  that  its  original  igneous  character  is  not  everywhere 
readily  apparent.  Least-altered  phases  show  a dark-gray  fine- 
grained rock  containing  numerous  dull  feldspar  phenocrysts  and  a 
few  quartz  crystals.  The  feldspars  prove  to  be  near  labradorite  in 
composition,  and  the  groundmass  is  largely  obscured  by  secondary 
minerals,  such  as  tourmaline,  quartz,  pyrite,  mica,  chlorite,  and  others. 
Some  movement  has  taken  place  along  the  walls  of  the  dike,  especially 
the  hanging  wall,  forming  a crushed  zone  1 to  6 inches  thick.  The 
dike  rock  is  heavily  charged  with  arsenical  pyrites  and  tourmaline  and 
contains  some  cassiterite  disseminated  through  it.  Locally  the  dike 
has  been  convened  into  large  masses  of  danburite  containing  radial 
groups  of  tourmaline  and  an  abundance  of  arsenopyrite.  Cassiterite 
is  inclosed  in  these  three  constituents,  but  is  visible  only  under  the 
microscope. 

The  wall  rock  of  the  dike  is  the  dense-textured  banded  argillaceous 
variety  of  the  Port  Clarence  limestone.  The  calcareous  portion  has 
been  converted  into  coarse  white  spar  containing  random  prisms  of 
tremolite;  the  argillaceous  bands  have  been  converted  into  matted 
aggregates  of  tremolite  fibers.  Finely  crystallized  cassiterite  occurs 
embedded  in  the  coarse  calc  spar  and  locally  is  extremely  abundant. 
Topaz  in  square  prisms  is  found  in  the  limestone  to  some  extent. 
Cassiterite  also  occurs  in  the  wall  rock  intimately  intergrown  with 
pocket-like  masses  of  danburite,  which  is  a calcium  borosilicate  re- 
lated to  topaz.  The  danburite  is  of  light  pinkish-gray  color,  with  a 
peculiar  vitreous  greasy  luster,  and  occurs  as  rude  ill-defined  columns 
in  rough  radial  arrangement.  Examination  of  the  danburite-cassit- 
erite  ore  in  thin  section  shows  that  the  cassiterite,  which  is  finely  idio- 
morphic,  lies  embedded  in  the  danburite,  and  contains  innumerable 
microlites  of  tourmaline.  The  danburite  incloses  some  small  patches 
of  calcite,  and  may,  like  the  cassiterite,  inclose  great  numbers  of 
minute  tourmaline  prisms.  These  bands  of  wall  rock,  which  carry 
tin  ore  and  show  marmorization  with  accompanying  development  of 
danburite,  topaz,  and  tremolite,  occur  on  both  foot  and  hanging  walls 
of  the  dike,  though  nowhere  more  than  6 inches  thick.  Tremolite, 
however,  persists  to  great  distances  from  the  dike,  though  in  lesser 
abundance.  Arsenopyrite  has  apparently  replaced  the  wall  rock  to 
some  extent  also,  as  solid  lumps  of  it  containing  only  tremolite  fibers 
have  been  found.  The  association  of  danburite  and  cassiterite  is 
unique  in  the  literature  of  tin  deposits.  To  establish  the  identity  of 
the  danburite  beyond  question  the  following  approximate  partial 


52 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


analysis  was  made  by  W.  T.  Schaller  on  the  purest  material  that  could 
be  obtained: 


Analysis  of  danburite  from  Dolcoath  lode,  Lost  River  region. 


SiOa— 
ALOs 
Fe2Oa 
CaO  _ 


47.  54 
3.  43 


21.02 


MgO 


1.  57 


b2o3 


a24.  03 


Specific  gravity,  2.98. 


97.  59 


Developments.-— At  the  time  of  visit  five  adits  had  been  driven  on 
the  Cassiterite  lode,  three  of  which  were  open  and  could  be  examined. 
Tunnel  B,  260  feet  above  Cassiterite  Creek,  was  180  feet  long.  The 
tunnel  follows  the  southern  margin  of  the  dike,  and  is  partly  in  lime- 
stone. At  45  feet  from  the  mouth  a drift  has  been  run  10  feet  to 
the  north,  crosscutting  the  lode.  Tunnel  A,  1,170  feet  above  the 
creek,  was  80  feet  long.  The  dike  is  soft  and  can  be  augered,  so  that 
an  advance  of  4 feet  a day  (single  shift)  is  easily  made.  Both  these 
adits  are  on  the  east  side  of  Cassiterite  Creek.  Tunnel  E,  driven  on 
the  Cassiterite  lode  10  feet  above  the  creek  level  on  the  west  side,  is 
100  feet  long.  A crosscut  9 feet  long  has  been  driven  50  feet  from 
the  mouth  of  the  adit.  The  Ida  Bell  dike  has  been  explored  by  an 
adit  55  feet  long,  at  the  end  of  which  a winze  69  feet  deep  was  sunk. 
This  is  now  filled  with  water. 

A few  hundred  feet  south  of  the  Cassiterite  lode  some  open  cuts 
and  adits,  now  caved  in,  were  opened  on  a porphyry  impregnated 
with  cassiterite.  No  surface  croppings  of  this  porphyry  body  are 
visible,  for  the  porphyry  is  buried  under  the  mantle  of  slide  rock 
covering  the  steep  slopes  of  the  region.  A shaft  50  feet  deep  was 
sunk  on  this  occurrence,  but  was  flooded  at  the  time  of  visit.  A 
number  of  open  cuts  have  partly  exposed  some  thin  but  rich  quartz 
veinlets  in  the  limestone.  A shaft  reported  to  be  18  feet  deep  was 
sunk  near  such  a vein  on  the  Jupiter  claim,  and  a drift  44  feet  long 
was  run  to  the  ledge,  but  both  were  also  under  water. 

The  developments  on  the  Dolcoath  dike  consist  of  four  cuts  opened 
at  intervals  along  a length  of  3,000  feet.  An  assay  of  ore  from  one 
of  the  crosscuts  was  reported  to  have  yielded  1.15  per  cent  of  tin. 

/Seaming  of  the  limestone. — The  most  striking  feature  in  the  vicin- 
ity of  the  Cassiterite  lode  is  the  vast  multitude  of  veinlets  that 
interlace  the  limestones  in  every  direction  (PI.  VII,  A).  The  area 
thus  affected  extends  for  1,000  feet  or  more  on  both  sides  of  the  stan- 

« Two  determinations  made  with  concordant  results  by  Messrs.  Chapin  and  Wherry 
under  the  direction  of  Prof.  Edgar  C.  Smith. 


ECONOMIC  GEOLOGY. 


53 


niferous  portion  of  the  dike.  On  the  basis  of  dominant  mineralogical 
composition  five  types  of  veinlets  can  be  discriminated — fluorite- 
amphibole,  plagiocla ~e-fluorite,  zinnwaldite-topaz,  topaz-fluorite,  and 
tourmaline-mica.  The  pure  types  occur,  but  innumerable  intermedi- 
ate and  transitional  forms  are  found  also. 

Veinlets  (PI.  VII,  B ),  only  one-half  inch  thick,  consisting  of  fluor- 
ite and  radial  amphibole,  are  paralleled  on  both  sides  by  altered  wall 
rock,  2 inches  wide,  sharply  delimited  against  marmorized  limestone 
containing  minute  fibers  of  tremolite.  The  wall  consists  of  fluor- 
ite, amphibole,  vesuvianite,  and  green  mica  irregularly  intergrown. 
Where  embedded  in  fluorite  the  amphibole  is  a deep-colored  variety, 
pleochroic  in  tones  of  brown-green  and  blue-green. 

Allied  to  the  veinlets  just  described  are  dense  white  veinlets  con- 
sisting essentially  of  fluorite  and  plagioclase.  Locally  they  contain 
hornblende  and  scattered  grains  of  pyrite  and  arsenopyrite.  They 
are  inclosed  by  dark-green  rock,  which  is  very  delicately  banded  by  thin 
white  bands  running  parallel  to  the  central  veinlet.  The  larger  bands 
are  a millimeter  in  width,  but  the  most  of  them  are  narrower,  and 
some  are  as  narrow  as  0.1  millimeter.  These  features  are  most  strik- 
ingly apparent  on  weather-etched  surfaces.  Small  seams  branching 
from  the  central  veinlet  cut  across  the  banded  rock.  The  metasomat- 
ically  altered  wall  rock  is  thus  elaborately  banded  at  but  few  places ; 
more  commonly  it  is  a structureless  green  rock.  In  thin  section  the 
central  veinlet  is  seen  to  be  composed  of  an  intimate  intergrowth  of 
fluorite  and  calcic  plagioclase  (as  calcic  at  least  as  AbjAn^,  with 
scheelite  as  an  accessory  mineral.  The  inclosing  rock  is  formed  of 
fluorite,  hornblende,  and  vesuvianite,  but  green  mica,  pju’oxene,  and 
calcic  plagioclase  also  occur,  and  arsenopyrite  and  cassiterite  are  pres- 
ent as  rare  accessories.  The  hornblende  and  vesuvianite  are  prone  to 
form  small  radial  groups.  The  narrow  white  bands  are  composed  of 
intergrowths  of  fluorite  and  plagioclase.  The  macroscopic  appear- 
ance of  the  banded  rock  immediately  recalls  the  orbules  and  banded 
veins  of  Tin  Creek,  and  this  external  resemblance  is  confirmed  by  the 
similarity  of  mineralogical  constitution  as  revealed  by  the  microscope. 
The  chemical  origin  of  the  banding  is  here  more  obviously  apparent. 

Veinlets  of  zinnwaldite  up  to  1 inch  in  thickness  are  common  in 
the  limestone.  Under  the  microscope  the  zinnwaldite  forms  radiating 
fanlike  groups  diverging  from  the  vein  walls.  The  mica  is  dirty 
greenish  and  somewhat  pleochroic  at  the  points  of  attachment.  Else- 
where it  resembles  muscovite.  Some  topaz  occurs  as  an  interstitial 
filling,  and  cassiterite  and  wolframite  are  rare  accessory  minerals.  In 
the  specimen  examined  optically  the  wall  rock  is  a cryptocrystalline 
limestone  exhibiting  only  a feeble  alteration.  Others,  however,  show 
an  energetic  fiuoritization  and  notable  increase  of  granularity.  An 


54 


TIN  DEPOSITS  OF  SEWAKD  PENINSULA,  ALASKA. 


analysis  of  the  zinnwaldite  has  been  made  by  W.  T.  Schaller®  in 
the  laboratory  of  the  Survey,  and  is  quoted  here  to  illustrate  the 
elaborate  composition  of  this  mica. 

Analysis  of  zinnwaldite  in  limestone  near  Cassiterite  lode , Lost  River  region. 


Si02 46.  80 

ALOs 24.50 

Fe,03 .50 

FeO 6.  35 

MnO 1.38 

CaO . 24 

Na20 1.73 

K20 9.  20 

Li20 3.  73 

H20 — ^ .88 

F 8.  63 

103.  94 

Less  0=2F 3.  63 


100.  31 

Topaz-fluorite  veinlets,  carrying  cassiterite  and  tabular  crystals  of 
wolframite,  have  produced  both  fluoritization  and  topazization  of  the 
adj  oining  limestone. 

On  the  south  side  of  the  Cassiterite  lode  tourmaline  veinlets  are 
common  in  the  limestone,  though  no  tourmaline  occurs  in  the  tin 
ore  of  the  dike  rock.  The  cause  of  this  peculiarity  is  not  known. 
This  type  of  veinlet  is  composed  of  white  mica,  blue  tourmaline,  and 
fluorite.  Some  carry  visible  cassiterite,  but  these  are  rare.  Micro- 
scopic examination  of  a stanniferous  veinlet  (one-half  inch  thick) 
showed  that  the  cassiterite  is  intergrown  with  scheelite,  calcite,  and 
mica  (zinnwaldite?)  and  embedded  in  a gangue  of  mica,  tourmaline, 
and  fluorite.  The  limestone  adjoining  the  tourmaline  stringers  has 
been  converted  into  a confused  intergrowth  of  green  and  indigo-blue 
tourmaline,  fluorite,  and  magnetite,  with  accessory  calcite,  vesuvian- 
ite,  green  mica,  and  amphibole,  forming  a rock  indistinguishable, 
texturally  and  mineralogically,  from  the  contact-metamorphosed 
limestone  of  Ear  Mountain. 

A feature  allied  to  the  seaming  of  the  limestone  by  the  veinlets  is 
found  in  an  outcrop  on  the  creek  200  feet  below  the  Cassiterite  lode, 
in  which  a zone  of  breeciated  limestone  has  been  recemented  by  vari- 
ous dark-colored  minerals  which  here  and  there  form  large  radial 
groups  3 to  4 inches  in  diameter.  The  cement  or  binding  material 
when  examined  optically  is  found  to  consist  chiefly  of  blue-green 
hornblende,  vesuvianite,  calcic  plagioclase  (A^An.,),  fluorite,  minor 
amounts  of  calcite,  and  accessory  scheelite. 


"Am.  Jour.  Sci.,  4th  ser.,  vol.  24,  1907,  p.  158. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  358  PL.  VIIJ 


A.  POLISHED  SURFACE  OF  SEAMED  LIMESTONE  SHOWING  INTENSE 
METASOMATISM  ACCOMPANYING  THE  VEINLETS  IN  LIMESTONE 
AND  NUMEROUS  SUBSIDIARY  VEINLETS  BRANCHING  FROM  MAIN 
VEINLET. 


B.  THIN  SECTION  OF  CASSITERITE  ORE. 
Magnification  12  diameters.  Radial  topaz  diverging  from  vein  wall. 


ECONOMIC  GEOLOGY. 


55 


To  sum  up  briefly:  In  spite  of  the  diversity  of  mineral  composi- 
tion of  the  various  veinlets  it  is  found  that  all  are  accompanied  by 
similar  intense  alterations  of  their  wall  rocks  (PL  VIII,  A).  They 
appear  to  be  of  practically  synchronous  origin,  except,  perhaps,  the 
tourmaline  veinlets,  and  the  smaller  seams  represent  leakages  along 
subsidiary  fractures.  A more  complete  interchange  of  material  be- 
tween wall  rock  and  solution  was  apparently  possible  in  the  minor 
seams,  for  vesuvianite  and  garnet  appear  in  them,  whereas  these  min- 
erals occur  only  in  the  meta somatically  altered  wall  rock  of  the 
larger  veinlets. 

Cassiterite  and  wolframite  quartz  veins. — It  is  a notable  feature 
that,  although  the  quartz  stringers  cutting  the  porphyry  dikes  con- 
tain cassiterite  and  wolframite  together,  those  cutting  the  limestone 
contain  either  cassiterite  alone  or  wolframite  alone,  and  in  large  pro- 
portions. Veinlets  of  such  diverse  composition  occur  not  many  hun- 
dred feet  apart.  They  average  only  a few  inches  in  thickness  and,  so 
far  as  is  now  known,  30  or  40  feet  in  length. 

The  cassiterite-quartz  veins,  while  rare  and  of  no  great  persistence, 
are  extraordinarily  rich  in  tin.  Cassiterite,  complexly  twinned,  oc- 
curs in  crystals  up  to  an  inch  in  size.  The  predominant  gangue  min- 
eral is  quartz,  with  which  are  associated  subordinate  amounts  of 
fluorite,  feldspar,  and  white  mica.  The  cassiterite  is  concentrated 
near  the  sides  of  the  vein,  which  is  frozen  to  the  wall  rock.  Locally 
a thin  band,  one-eiglith  inch  thick,  of  delicate  radial  topaz  inter- 
venes between  the  quartz  gangue  and  the  altered  wall  rock.  Thin 
sections  cut  from  this  portion  of  the  ore  show  groups  of  topaz  prisms 
diverging  from  the  wall  of  the  vein  (PL  VIII,  B).  Closely  asso- 
ciated with  them  are  fluorite,  white  mica  in  well-defined  plates, 
quartz,  and  cassiterite.  The  wall  rock  consists  of  a fine-grained  ag- 
gregate of  fluorite,  topaz,  and  mica.  Farther  away  from  the  vein  the 
limestone  is  marmorized  and  transfixed  with  tremolite  needles.  The 
filling  of  the  veinlets  branching  off  from  the  cassiterite-quartz  vein 
is  not  quartz,  but  is  chiefly  white  mica.  In  the  country  rock  adjoin- 
ing the  cassiterite-quartz  vein,  veinlets  consisting  essentially  of  white 
mica  and  lamellated  plagioclase  are  common,  and  some  of  these  are 
metalliferous.  In  their  central  portions  they  carry  small  amounts  of 
galena,  chalcopyrite,  pyrrhotite,  and  sphalerite.  The  wall  rock  ad- 
joining these  veinlets,  which  average  perhaps  one- fourth  inch  in 
thickness,  is  altered  to  fluorite  and  aggregates  of  scaly  green  mica. 

Some  quartz  stringers  carrying  considerable  wolframite  have  been 
found  cutting  the  limestone.  The  gangue  material  is  dominantly 
quartz,  but  fluorite,  white  mica,  and  albite  also  occur.  The  altered 
wall  rock  consists  of  fluorite,  green-blue  hornblende,  vesuvianite, 
green  mica,  and  garnet,  with  scheelite  and  cassiterite  as  rare  accessory 
minerals  (Pl.  IX,  B).  Sphalerite  and  chalcopyrite  occur  dissemi- 


56  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

nated  through  the  metamorphosed  wall  rock,  though  absent  from  the 
quartz  veins  themselves.  The  zone  of  metasomatism  is  sharply 
bounded  by  white  saccharoidal  limestone  containing  sporadic  prisms 
of  tremolite  (PL  IX,  A). 

The  cause  of  the  segregation  of  the  cassiterite  and  wolframite  into 
separate  veinlets  is  not  known.  On  the  hill  between  Lost  River  and 
Cassiterite  Creek  a prospect  trench  has  opened  a tin-bearing  veinlet 
1 inch  to  6 inches  thick  for  a length  of  30  feet.  At  one  end  the  vein- 
let  can  be  seen  to  pinch  out.  Throughout  its  length  it  is  unusually 
rich  in  cassiterite  and  carries  some  wolframite  and  arsenopyrite.  The 
gangue  is  composed  essentially  of  topaz,  fluorite,  and  zinnwaldite, 
arranged  in  a rudely  banded  structure.  The  middle  band  is  the 
most  distinctly  defined,  though  only  one-half  inch  broad,  and  con- 
sists chiefly  of  topaz  imperfectly  interlocking  along  a central  line. 
The  wall  rock  of  this  veinlet  is  highly  altered  and  is  impregnated 
to  some  extent  with  chalcopyrite,  pyrite,  and  sphalerite.  The  study 
of  this  occurrence  suggests  that  the  simple  quartz  veins  are  due  to  a 
sort  of  differentiation  from  the  primary  solutions  that  deposited 
fluosilicates,  and  that,  accompanying  this  change,  a segregation  of 
cassiterite  from  the  wolframite  may.  have  taken  place. 

Metasomatic  'processes. — The  Lost  River  occurrences  throw  some 
light  on  the  metasomatism  produced  by  stanniferous  solutions  acting 
on  a nearly  pure  limestone.  In  the  zone  of  most  intense  activity 
fluorine  has  effected  a complex  expulsion  of  the  carbon  dioxide  with 
the  production  of  abundant  fluorite.  On  the  assumption  that  the 
calcium  remains  constant  and  is  combined  as  fluorite,  this  means  a 
loss  in  volume  of  34  per  cent.  This  shrinkage  appears  to  have  been 
amply  compensated  for  by  the  production  of  topaz,  hornblende, 
vesuvianite,  mica,  plagioclase,  and  garnet,  all  of  which  involve  an 
introduction  of  material,  chiefly  alumina  and  silica,  with  some  FeO, 
Na20,  K20,  and  Li20.  Beyond  the  zone  of  fluoritization  the  lime- 
stone has  been  marmorized  and  some  tremolite  produced.  The 
transition  between  the  two  zones  is  abrupt,  and  the  difference  of 
the  amphiboles  in  them  is  a characteristic  feature.  The  colorless 
tremolite,  which  is  less  abundant  than  the  deep  blue-green  hornblende, 
has  doubtless  been  produced  by  the  recrystallization  of  impurities  in 
the  original  limestone.  Where  the  stanniferous  solutions  contained 
boron,  alkali  tourmaline  has  commonly  been  developed  as  a meta- 
somatic mineral.  At  the  Dolcoath  dike  the  solutions  appear  to  have 
been  unusually  rich  in  boron,  and  extensive  danburitization  lias  taken 
place,  with  accompanying  development  of  cassiterite,  tremolite,  tour- 
maline, and  topaz.  Marmorization,  too,  has  locally  been  intense, 
with  the  production  of  calcite  individuals  up  to  an  inch  in  size. 

The  metasomatic  processes  outlined  in  the  preceding  paragraph 
are  of  a synthetic  nature  and  have  caused  the  formation  of  various 


A.  POLISHED  SURFACE  OF  WALL  ROCK  ADJOINING  WOLFRAMITE-QUARTZ  VEIN. 
Showing  marked  contrast  between  the  marmorized  limestone  and  the  metasomatically  altered  limestone. 


B.  THIN  SECTION  OF  WALL  ROCK  ADJOINING  QUARTZ-WOLFRAMITE  VEIN. 
Magnification  32  diameters.  Showing  an  intergrowth  of  hornblende,  vesuvianite,  and  fluorite. 


ECONOMIC  GEOLOGY. 


57 


complex  silicates,  some  of  which,  like  topaz,  danburite,  vesuvianite, 
and  hornblende,  have  not  been  described  previously  as  alteration 
products  in  limestone  adjoining  fissure  veins.  Topaz,  according  to 
Rosenbusch,®  is  characteristic  of  the  pneumatolytic  contact  zones  of 
many  granites.  Danburite  has  recently  been  described  as  a con- 
stituent in  some  of  the  numerous  contact-metamorphic  deposits  of 
Japan.6  Vesuvianite  is  a typical  contact-metamorphic  mineral,  and 
hornblende  is  common  in  the  metamorphic  aureoles  of  many  granites. 
Tremolite,  a common  contact-metamorphic  mineral,  has,  however, 
been  recorded  by  Lindgren  c from  the  Clifton-Morenci  district  as  a 
metasomatic  product  in  limestone  adjoining  fissure  veins,  and  the 
unusual  and  significant  character  of  this  alteration  has  been  pointed 
out,  Tremolite,  as  has  been  shown,  is  one  of  the  commonest  products 
of  the  metasomatic  activity  of  stanniferous  solutions  circulating  in 
limestone,  but  only  in  the  zone  of  least  intense  activity.  To  sum  up 
briefly,  the  metasomatic  alteration  accompanying  cassiterite  veins  in 
limestone,  as  exemplified  by  these  Alaskan  occurrences,  is  closely 
allied  to  contact  metamorphism.  The  wall  rock  immediately  ad- 
joining the  vein  is  characterized  by  the  addition  of  material  and  the 
formation  of  fluo-,  boro-,  and  alumino-silicates.  This  zone  passes 
outward  into  one  showing  the  features  of  simple  thermal  meta- 
morphism— marmorization  with  the  production  of  sporadic  tremolite. 

W olfrcimite-topaz  lode. — A unique  mineral  deposit  is  exposed  op- 
posite the  mouth  of  Tin  Creek  in  an  open  cut  on  the  ridge  between 
Lost  River  and  Left  Fork.  The  surface  indications  show  that  the 
mineralization  has  taken  place  along  a fault,  running  approximately 
east  and  west,  which  has  brought  two  slightly  dissimilar  limestones 
into  juxtaposition.  Some  brecciation  is  apparent  along  this  line. 
The  open  cut  shows  stringers  of  ore  occurring  in  a belt  1 foot  thick, 
forming  a stringer  lode.  The  ore  minerals  consist  of  wolframite, 
galena,  .and  stannite,  and  are  embedded  in  a gangue  of  radial  topaz 
associated  with  some  deep-purple  fluorite.  The  stannite  is  usually 
intercrystallized  with  the  galena  and  is  of  a brown-black  color.  It 
reacts  for  tin,  copper,  zinc,  iron,  and  sulphur.  The  topaz  forms  fine 
spherulitic  aggregates,  which  may  in  places  attain  a diameter  of  half 
an  inch,  but  as  a rule  are  very  small  and  are  crystallized  in  delicate 
radial  groups.  The  high  specific  gravity  of  topaz  (3.5)  gives  the 
ore  rock  an  unusually  heavy  weight.  The  surface  ore  is  stained  black 
by  manganese  minerals  produced  by  the  decomposition  of  wolframite. 
Some  azurite  is  present  also,  and  is  doubtless  derived  from  the  copper 

a Mikroskopische  Physiographie,  vol.  1,  pt.  2,  Stuttgart,  1905,  p.  139. 

b Beitrage  zur  Mineralogie  von  Japan,  No.  3,  Tokyo,  1907,  p.  102. 

c Lindgren,  W.,  Copper  deposits  of  Clifton-Morenci  district,  Arizona : Prof.  Paper  U.  S. 
Geol.  Survey  No.  43,  1905,  p.  176. 


. 58 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


in  the  stannite.  An  assay  0 of  a sample  of  this  ore  submitted  by  the 
Survey  gave  a return  of  22.9  ounces  of  silver  to  the  ton. 

The  gangue  material  was  identified  optically  as  topaz  from  its 
similarity  to  that  associated  with  the  tin  ore  on  Cassiterite  Creek. 
This  determination  was  confirmed  by  an  approximate  quantitative 
analysis  made  by  W.  T.  Schaller,  with  results  as  follows : 

Analysis  of  topaz  from  wolframite-topaz  lode,  near  Tin  Greek. 


Si02 30.  27 

ALOs 54.66 

CaO 1. 16 

MgO Trace. 

F * 17.  26 

H20,  alkalis Not  clet. 


103.  35 

Less  0=2  F 7.  27 


96.  08 

The  wall  rock  of  the  topaz  lode  consists  of  a dense  cryptocrystal- 
line limestone  which  shows  no  evidence  of  metasomatic  alteration. 
The  topaz  lode  is  remarkable  in  two  respects — it  is  the  first  recorded 
instance  of  topaz  as  a fissure- vein  filling  and  as  the  gangue  material 
of  sulphide  minerals.  Topaz  is  common  in  the  greisen  adjoining  cas- 
siterite veins  and  in  certain  metasomatically  altered  quartz  porphyry 
dikes,  but  has  not  hitherto  been  noted  as  a vein- forming  mineral.  It 
is  regarded  by  Vogt *  & as  distinctive  of  the  cassiterite  veins  in  contrast 
with  the  ordinary  sulphide-ore  veins  (filcns  plombiferes) . The  ab- 
sence of  metasomatic  alteration  in  the  limestone  adjoining  the  topaz 
lode  is  noteworthy,  but  it  will  be  recalled  that  some  of  the  zinnwald- 
ite-topaz  veinlets  in  the  vicinity  of  the  Cassiterite  lode  show  a similar 
lack  of  action  on  their  wall  rocks. 

The  stannite  in  the  above-described  wolframite-topaz  lode  is  the 
only  known  verified  occurrence  of  this  mineral  in  the  Alaskan  tin 
region.  Stannite  is  not  a valuable  tin- ore  mineral,  both  on  account 
of  its  relatively  low  tin  content  (30  per  cent  compared  to  78  per  cent 
in  cassiterite)  and  its  difficult  metallurgical  treatment.  It  is  a rather 
favorite  object  of  search  with  the  prospector,  chiefly  because  of  the 
fascination  which  its  unknown  character  exercises;  and  in  conse- 
quence pyrite  and  pyrrhotite  are  commonly  mistaken  for  stannite. 
It  is,  however,  a mineral  whose  identity  can  be  established  only  by 
careful  chemical  examination. 

OTHER  MINERAL  DEPOSITS. 

Alaska  Chief  'property. — The  Alaska  Chief  claim  is  situated  about 
44  miles  from  Bering  Sea,  on  Rapid  River,  the  large  western  branch 


n Made  by  Ledoux  & Co.,  of  New  York. 

6 Genesis  of  ore  deposits  ; special  publication  of  Am.  Inst.  Min.  Eng.,  1902,  p.  666. 


ECONOMIC  GEOLOGY. 


59 


of  Lost  River.  The  workings  are  on  a small  gulch  tributary  to 
Rapid  River.  The  country  rock  is  a tough,  fine-grained  limestone 
of  the  Port  Clarence  formation,  lying  nearly  horizontal.  Locally* the 
strata  are  buckled  and  show  crushing  in  the  crest  of  the  buckles.  A 
fault  breccia  15  feet  wide,  consisting  of  small  angular  fragments  of 
limestone  cemented  together  by  white  calc  spar,  is  exposed  in  the 
creek  one-third  mile  west  of  the  mine.  Basalt,  in  the  form  of  a nar- 
row dike  1 foot  thick,  is  the  only  other  rock  known  to  be  in  place  in 
the  near  vicinity  of  the  mine.  A few  thousand  feet  to  the  east  a 
number  of  quartz  porphyry  dikes  can  be  seen  cutting  the  limestone. 

The  original  shaft  was  sunk  in  a heavy  body  of  porous  red  iron 
oxide  containing  galena,  reported  to  be  12  feet  thick.  At  a depth  of 
35  feet  work  was  suspended.  An  adit  143  feet  long  driven  85  feet 
below  the  collar  of  the  shaft  encountered  the  same  ore  body  50  feet 
below  the  bottom  of  the  shaft.  The  ore  was  still  oxidized.  About 
7 feet  of  low-grade  galena  ore  was  exposed. 

On  the  east  side  of  the  gulch  a devious  tunnel,  about  600  feet  in 
length,  was  driven  to  catch  another  body  of  galena  indicated  on  the 
surface.  The  tunnel  follows  a zone  of  crushed  limestone,  bounded  in 
many  places  by  fine  walls  marked  with  striae.  The  “ ledge  matter  ” 
consists  of  small  fragments  of  limestone  bound  together  by  coarse 
calc  spar,  clay,  and  red  iron  oxide.  No  ore  was  encountered.  The 
tunnel  on  the  west  side  of  the  gulch  was  then  commenced,  and  the 
ore  body  already  mentioned  was  struck  late  in  August,  1907. 

Idaho  claim. — A few  hundred  yards  below  the  mouth  of  Tin  Creek 
a copper  prospect  has  been  opened  on  the  edge  of  the  15-foot  bench 
fronting  Lost  River,  and  at  the  time  of  visit  enough  work  had  been 
done  to  expose  the  face  of  ore  at  this  point.  The  deposit  occurs  in 
an  irregular  shattered  zone  in  the  limestone,  15  feet  wide  and  includ- 
ing numerous  horses  of  unmineralized  limestone.  The  ore  mineral  is 
chalcopyrite,  associated  with  abundant  pvrrhotite  (magnetic  iron 
pryites),  and  occurs  in  a gangue  of  calcite,  fluorite,  and  small  frag- 
ments of  slickensided  rock.  Some  of  the  fluorite  is  rose-tinted  and 
is  locally  known  as  ruby  quartz.  Stripping  has  shown  that  the  same 
ore  body  extends  at  least  50  feet  to  the  east,  where  a strong  gossan  has 
been  uncovered.  The  relatively  great  width  of  the  deposit,  com- 
bined with  the  low  chalcopyrite  tenor  and  the  abundance  of  pyrrho- 
tite,  reduces  the  copper  percentage  to  a small  figure. 

On  Tin  Creek  a galena  prospect  has  been  opened  on  some  gossan 
croppings  at  an  altitude  of  1,100  feet,  800  feet  above  the  bed  of  the 
creek.  The  deposit  occurs  in  a fracture  zone  in  the  limestone,  which 
has  been  coarsely  recrystallized  in  the  immediate  vicinity,  forming 
spar  crystals  up  to  an  inch  in  size.  The  gossan  consists  of  honey- 
combed masses  of  iron  oxide  containing  abundant  galena  and  numer- 
ous white  and  colorless  crystals  of  cerusite  (lead  carbonate).  It  was 


60  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

planned  to  prove  the  value  of  this  deposit  during  the  winter  of  1907 
and  1908. 

A small  trench,  650  feet  below  the  galena  prospect,  has  been  dug 
in  the  effort  to  locate  the  bed-rock  source  of  some  loose  bowlders  com- 
posed of  arsenopyrite  flecked  with  a small  amount  of  cupriferous 
pyrite.  Assays  made  in  Nome  are  reported  to  have  yielded  $12  to  the 
ton  in  gold.  Some  stibnite  in  a gangue  of  purple  fluorite  has  been 
found  in  the  saddle  at  the  head  of  Tin  Creek. 

ORIGIN  OF  THE  ORES. 

The  injection  of  the  quartz  porphyry  dikes  represents  the  final 
intrusive  activity  of  an  underlying  granite  magma,  of  which  a 
portion  is  now  exposed  by  erosion  on  Tin  Creek.  Fracturing  of  the 
dikes,  accompanied  by  shattering  of  the  adjacent  limestone,  took 
place  after  their  consolidation,  and  an  energetic  mineralization 
ensued.  As  shown  by  the  vein  fillings  and  metasomatic  alterations 
the  ore-depositing  solutions  were  characterized  by  their  richness 
in  fluorine,  aluminum,  silicon,  calcium,  tin,  tungsten,  iron,  man- 
ganese, arsenic,  sulphur,  lithium,  potassium,  and  sodium,  but  con- 
tained also  copper,  lead,  and  zinc,  and  locally  boron  in  abundance. 
The  state  of  combination  of  the  various  elements  in  solution  is  not 
known.  The  vein  material  includes  various  silicates,  such  as  topaz, 
zinnwaldite,  tourmaline,  and  albite,  and  proves  that  conditions 
unusual  in  the  formation  of  the  ordinary  types  of  veins  prevailed. 
Albite  and  tourmaline  are  commonly  regarded  as  indicative  of  the 
magmatic  derivation  of  vein-forming  waters,  and  topaz  and  zinn- 
waldite are  the  two  most  characteristic  of  the  so-called  pneumatolytic 
minerals.  The  presence  of  topaz  in  the  vein  matter  itself  is  some- 
what unusual,  inasmuch  as  this  mineral,  although  common  in  the 
greisen  adjoining  quartz-cassiterite  veinlets  in  granite  as  a replace- 
ment of  feldspar,  is  comparatively  rare  as  a fissure  filling.  Of  the 
minerals  contained  in  the  veinlets  as  Cassiterite  Creek  all,  with  the 
notable  exception  of  quartz,  have  also  developed  metasomatically  in 
the  limestone.  It  is  noteworthy  that  cassiterite,  though  present  in 
large  proportions  in  many  of  the  veinlets,  appears  only  in  insignificant 
amounts  in  the  intensely  altered  wall  rock.  In  addition  hornblende, 
vesuvianite,  garnet,  and  others  were  formed,  and  prove  that  condi- 
tions allied  to  those  obtaining  during  contact  metamorphism  pre- 
vailed. The  stanniferous  solutions  were  therefore  presumably  of 
magmatic  origin  and  at  high  temperature  and  pressure. 

The  abundance  of  fluorine  compounds — fluorite,  topaz,  and  zinn- 
waldite— is  in  harmony  with  Daubree’s  generalization®  that  fluorine 
is  the  active  agent  in  the  formation  of  tin  deposits.  According  to 


Daubree,  A.,  G^ologie  experimentale,  p.  38. 


ECONOMIC  GEOLOGY. 


61 


his  theory  cassiterite  is  produced  by  the  mutual  decomposition  of 
the  vapors  of  water  and  stannic  chloride  reacting  as  follows: 

• SnCl4+2H20=Sn02+4HCl. 

He  was  actually  able  to  synthesize  cassiterite  in  this  way. 

According  to  analogy  we  would  expect— 

SnF4+2H20=Sn02+4HF. 

Cassiterite  has  been  produced  at  red  heat  by  Deville  and  Caron  ° in 
conformity  to  this  equation.  Quartz  can  be  synthesized  according 
to  an  analogous  reaction.  In  recent  years  Vogt & has  been  a vigorous 
exponent  of  the  pneumatolytic  or  gas-aqueous  origin  of  cassiterite 
deposits.  He  conceives  that  hydrochloric  and  hydrofluoric  acids 
acting  on  a cooling  granite  magma  effect  an  acid  extraction  of  tin 
and  the  various  elements  associated  with  it.  Gaseous  conditions  are 
therefore  considered  as  dominant  during  the  formation  of  cassiterite 
bodies,  and  the  final  individualization  of  the  minerals  is  held  to  be 
due  to  the  reactions  of  Daubree’s  experiments. 

Certain  facts  in  the  Lost  River  area  suggest  that  fluorine  is  not, 
however,  absolutely  essential  to  the  formation  of  cassiterite.  On  the 
Dolcoath  dike  some  of  the  richest  ore  is  intergrown  with  danburite 
(CaB2(Si04)2)  and  the  limestone  shows  no  fluorite,  although  the 
latter  is  common  in  the  vicinity  of  the  Cassiterite  lode.  Moreover, 
the  cassiterite  includes  multitudes  of  tourmaline  microlites,  so  that 
there  is  obviously  a closer  association  of  the  tin  with  boron  than  with 
fluorine.  On  the  other  hand,  the  wolframite-topaz  lode,  with  its 
content  of  galena  and  stannite,  proves  that  tin  and  abundant  fluorine 
may  coexist  in  the  same  solution  and  cassiterite  not  be  formed. 

PLACERS. 

BUCK  CREEK. 

Developments  subsequent  to  1905  have  revealed  few  new  facts  of 
interest  in  regard  to  the  placers  of  Buck  Creek.  The  gravels  have  a 
length  of  about  4 miles  and  are  shallow.  Work  below  the  mouth  of 
Sutter  Creek  has  shown  that  the  gravel  in  that  part  of  the  stream  is 
from  120  to  160  feet  wide,  averaging  about  125  feet.  The  width  of 
the  pay  streak  is  not  known.  A pit  having  a mean  depth  of  5 feet, 
from  which  48  tons  of  concentrates  have  been  extracted,  has  demon- 
strated that  the  gravel  may  run  as  high  as  25  pounds  per  cubic  yard. 
The  gravel  is  a comparatively  fine  wash  and  bowlders  are  rare,  the 


a Compt.  Rend.,  vol.  46,  1858,  p.  764. 
b Zeitschr.  prakt.  Geologie,  1895,  p.  475. 


62 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA, 


largest  noted  consisting  of  greenstone  about  a foot  in  diameter.  The 
richest  gravel  rests  immediately  upon  bed  rock  and  is  exceedingly 
clayey  and  toughly  bound  together.  It  gives  difficulty  in  washing, 
the  clay  having  a tendency  to  roll  up  in  balls  and  carry  cassiterite 
nuggets  over  the  sluice  boxes.  The  bed  rock  is  a broken  shale  or  slate, 
very  clayey,  but  contains  no  cassiterite.  On  Sutter  Creek,  the  large 
southern  branch  of  Buck  Creek,  there  is  a considerable  body  of  gravel, 
and  the  discovery  of  stream  tin  has  recently  • been  reported  on  it. 
The  other  tributaries,  gulches,  and  “ benches  ” of  Buck  Creek  contain 
little  or  no  gravel,  at  least  in  amounts  sufficient  to  warrant  an  outlay 
for  the  purpose  of  placer  mining. 

The  stream  tin  of  Buck  Creek  is  clearly  derived  from  the  erosion 
and  concentration  of  the  cassiterite  occurring  in  the  quartz  stringers 
so  abundant  throughout  the  area.  This  source  was  partly  supple- 
mented by  the  cassiterite  occurring  in  the  actinolite  rock,  and  to  a 
lesser  extent  by  that  contained  in  the  quartz  porphyry  dikes.  As 
these  bed-rock  sources  are  known  to  occur  in  place  on  the  summit  of 
the  hills  at  the  head  of  Buck  Creek,  it  is  probable  that  some  of  the 
creeks  flowing  into  Lopp  Lagoon  carry  stream  tin.  But  whether 
cassiterite  is  present  in  these  streams  in  payable  quantities  is  purely 
a matter  of  accurate  sampling,  and  not  of  opinion  or  theory — an  idea 
which  prevails  in  certain  quarters  to  th§  detriment  of  the  region. 

Two  companies  were  in  operation  on  Buck  Creek  during  1907,  but 
on  account  of  a number  of  adverse  circumstances  the  yield  was  less 
than  was  expected.  Placer  mining  was  confined  to  a small  strip  just 
below  the  mouth  of  Sutter  Creek,  and  the  total  output  of  the  year 
was  approximately  50  tons  of  concentrates. 

At  the  beginning  of  the  season  the  American  Tin  Mining  Company 
was  working  its  ground  by  means  of  an  automatic  scraper  and  belt 
conveyor  operated  by  a 35-horsepower  oil-burning  engine.  Early  in 
August,  however,  extortionate  freight  rates  on  the  transportation  of 
crude  oil  from  Nome  to  York  and  the  imperfect  adaptation  of  the 
scraper  to  the  character  of  the  gravel  necessitated  a change  in  the 
method  of  working.  Shoveling  in  was  then  adopted,  with  results  at 
least  more  satisfactory  than  those  attained  with  machinery.  The 
other  company  also  employed  the  shoveling-in  method,  and  the  tail- 
ings were  removed  by  a horse  and  scraper. 

GROUSE  CREEK. 

During  the  summer  of  1907  assessment  work  was  done  on  a num- 
ber of  claims  on  Grouse  Creek  and  two  of  its  tributaries,  Sterling 
and  Skookum  creeks.  The  results  are  not  known.  Some  gold  sifted 
out  of  the  stream-tin  concentrates  from  Sterling  Creek  was  flat,  coarse, 
and  not  greatly  waterworn,  and  had  quartz  still  adhering  to  it. 


RESUME  AND  CONCLUSIONS. 


63 


FAIRHAVEN  DISTRICT. 

A sample  of  black-sand  concentrates  from  Humboldt  Creek  sent 
in  to  the  office  for  determination  proved  to  be  a rich  tin  ore  con- 
taining less  than  $5  per  ton  in  gold.  About  two-thirds  of  the  sample 
was  pyrite.  Another  sample  of  concentrates  sent  in  from  Kougarok 
River  was  found  to  contain  considerable  cassiterite,  but  far  less  than 
the  Humboldt  Creek  sample.  It  carried,  however,  85  ounces  of  gold 
per  ton  and  contained  66  per  cent  of  pyrite  and  about  10  per  cent  of 
magnetite.  As  the  headwaters  of  Humboldt  Creek  drain  the  Hot 
Springs  granite  area,  the  tin  was  probably  derived  from  that  region. 
Collier  states  that  samples  of  tin  ore  purporting  to  come  from  it  were 
brought  to  Nome  late  in  the  season  of  1902. 

RESUME  AXI)  CONCLUSIONS. 

Four  localities  in  the  western  part  of  Seward  Peninsula  are  being 
prospected  for  lode  tin  at  the  present  time.  From  one  stream — 
Buck  Creek — placer  tin  is  actually  being  extracted,  and  an  output  of 
approximately  50  tons  of  concentrates  was  attained  in  1907. 

The  sedimentary  rocks  of  the  York  region  comprise  a series  of 
slates  of  unknown  but  probabty  early  Paleozoic  age,  a thick  volume 
of  tliin-bedded  limestone  of  Ordovician  age  (Port  Clarence  lime- 
stone), and  crystalline  limestone  of  Carboniferous  age.  At  Ear 
Mountain  contorted  limestones  and  lime-mica  schists  prevail.  These 
rocks  are  intruded  by  a number  of  granite  masses,  which,  though  ap- 
pearing in  isolated  stocks,  show  by  the  many  features  that  they  pos- 
sess in  common  that  they  belong  to  the  same  irrupt ive  magma.  The 
granites  are  coarse-grained  types  with  large  porphyritic  feldspars 
and  quartz  which  is  commonly  of  a conspicuously  smoky  character. 
They  were  unusually  rich  in  volatile  constituents,  among  which  boron, 
fluorine  together  with  chlorine,  and  iron  were  the  most  prevalent,  and 
they  are  therefore  characteristically  surrounded  by  pneumatolytic 
contact  aureoles.  Large  amounts  of  the  magmatic  emanations  wTere 
retained  by  the  limestones  in  such  minerals  as  tourmaline,  axinite, 
ludwigite,  hulsite,  paigeite,  boron  vesuvianite,  magnetite,  heden- 
bergite,  fluorite,  scapolite,  and  chondrodite. 

Complementary  contact  phenomena  occur  at  Cape  Mountain,  where 
giant  granite  selvages  are  overlain  by  fluoritic  and  sea  politic  pyr- 
oxene hornfels  containing  accessory  scheelite.  These  phenomena 
are  regarded  as  showing  on  the  one  hand  the  effect  of  the  mineralizers 
on  the  crystallization  of  the  magma,  and  on  the  other  hand  their  effect 
in  producing  intense  metasomatic  action  on  the  adjoining  limestone. 
Essentially  similar  metasomatism  was  produced  by  a pegmatite  intru- 
sive in  the  marble  surrounding  the  granite  stock  of  Brooks  Mountain. 
Along  Tin  Creek  a novel  type  of  contact  metamorphism  which  has 


64 


TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 


produced  perfect  orbicular  forms  has  occurred.  The  orbules  are 
allied  in  their  origin  to  garnet- vesuvianite  masses,  which  have  injected 
small  banded  apophyses,  as  it  were,  into  the  inclosing  limestone.  The 
supply  ducts  for  the  orbules  consist  of  curious  banded  veins  composed 
of  fluorite,  calcic  plagioclase,  and  pyroxene,  with  accessory  arsenopy- 
rite,  cassiterite,  and  scheelite. 

The  tin  deposits  are  genetically  associated  with  the  granitic  intru- 
sives.  Cassiterite  occurs  in  a variety  of  ways : 

(1)  In  a tourmaline-axinite  hornfels. 

(2)  In  beds  of  actinolite  rock  which  are  probably  interstratified 
with  slates. 

(3)  In  tourmalinized  margins  of  granite  masses  and  granitic  dikes. 

(4)  In  mineralized  quartz  porphyry  dikes. 

(5)  In  quartz  veins  cutting  granite  and  accompanied  by  impregna- 
tion of  the  adjoining  granite. 

(6)  In  quartz  stringers  cutting  slates  and  limestones. 

In  addition,  tin  is  found  to  be  present  as  paigeite  (an  iron-tin 
borate)  in  lime-silicate  hornfels. 

At  Ear  Mountain  cassiterite  occurs  in  a contact-metamorphosed 
limestone  consisting  essentially  of  tourmaline,  axinite,  and  actinolite, 
but  it  is  not  found  in  any  of  the  other  pneumatolytic  contact  rocks  of 
the  region.  This  is  a fact  of  considerable  interest  from  the  stand- 
point of  ore  genesis.  The  stanniferous  granite  magma  was  rich  in 
halogens  and  boron,  and  theoretically  the  limestones  are  favorable  loci 
for  the  precipitation  of  cassiterite.  By  the  action  of  stannic  chloride 
(SnCl4)  vapor  on  lime  Daubree  ° was  able  to  synthesize  cassiterite. 
The  limestone  contacts  might  therefore  be  expected  to  show  this  min- 
eral. But  as  a matter  of  fact  the  contact  rocks,  although  rich  in  pneu- 
matolytic minerals,  are  as  a rule  barren  of  tin.  The  advent  of  the 
cassiterite  was  postponed  to  a later  stage,  and  where  evidence  can  be 
obtained  as  to  the  relative  ages  of  intrusion  and  mineralization  the 
latter  postdates  the  injection  of  the  quartz  porphyry  or  rhyolitic 
dikes.  This  would  appear  to  indicate  that  a long  period  of  prelim- 
inary concentration  was  taking  place  in  the  cooling  magma. 

The  rarity  of  cassiterite  as  a contact-metamorphic  mineral  the 
world  over  is  anomalous.  As  far  as  the  writer  is  aware  the  only 
deposit  in  which  it  is  unequivocally  of  contact-metamorphic  origin  is 
that  in  the  Dartmoor  Forest,  Devonshire,  England,  described  by 
Busz.&  At  this  locality  hornfels  adjoining  the  granite  contact  consists 
essentially  of  light-colored  mica,  quartz,  and  tourmaline  with  innu- 
merable grains  and  minute  crystals  of  cassiterite  scattered  throughout 
the  rock. 


° Compt.  Rond.,  vol.  30,  1854,  p.  138. 
b Busz,  K.,  Neues  Jalirb.,  Beil.  Band  13,  1899,  p.  100. 


RESUME  AND  CONCLUSIONS. 


65 


At  the  St.  Dizier  mine,0  in  Tasmania,  cassiterite  occurs  in  a mag- 
netite-silicate rock  of  the  Kristiania  type,  but  it  is  not  entirely  clear 
whether  the  cassiterite  is  contemporaneous  with  the  other  constitu- 
ents. According  to  Twelvetrees  6 the  tin-bearing  rock  at  the  Stony 
Ford  mine,  Tasmania,  is  a band  of  quartz-chlorite  rock,  charged  with 
pink  garnets,  pyrite,  some  blende  and  chalcopyrite,  and  cassiterite. 
This  is  regarded  as  probably  resulting  from  the  contact  metamorph- 
ism of  slates  and  sandstone.  At  Pitkaranta,  Finland,  cassiterite  oc- 
curs lining  druses  along  a definite  formation  consisting  of  lime-silicate 
rock  (“  skarn  ”)  that  was  produced  in  early  pre-Cambrian  time  by 
the  contact  metamorphism  of  a limestone.  The  tin  ore,  however,  is 
connected  with  the  intrusion  of  the  Rapikiwi  granite  of  late  pre- 
Cambrian  age,  and  is  regarded  as  of  contact -metamorphic  origin, 
being  due  to  magmatic  solutions  flowing  along  pervious  contacts. 
This  conception  c of  the  genesis  of  the  deposits  would  practically  ex- 
tend the  term  contact  metamorphism  to  all  deposits  formed  by  juvenile 
waters  of  high  temperature. 

A remarkable  similarity,  both  mineralogic  and  geologic,  exists  be- 
tween these  deposits  and  those  of  Schwarzenberg  in  Saxony ,d  where 
cassiterite  occurs  as  a secondary  impregnation  in  a salite-tremolite 
rock  which  at  some  distance  from  the  contact  encircles  a granite  mass. 
Dalmer,  however,  would  include  these  deposits  as  a phase  of  contact 
metamorphism,  using  that  term  in  its  largest  sense.  From  this  re- 
view it  would  appear  that  stanniferous  contact  deposits  of  the  Kris- 
tiania type  are  of  extremely  rare  occurrence.  One  such  deposit  of 
commercial  importance  has  yet  to  be  found.  This  is  certainly  a sur- 
prising fact  in  view  of  the  commonly  accepted  theory  of  the  pneu- 
matolytic  origin  of  the  majority  of  tin-ore  deposits. 

The  Alaskan  tin  deposits  exhibit  a number  of  unique  features. 
These  include  the  association  of  cassiterite  and  arsenopyrite  in  a 
gangue  of  actinolite ; the  intergrowth  of  cassiterite  with  the  rare  cal- 
cium borosilicate,  danburite;  and  the  occurrence  of  an  argentiferous 
wolframite-topaz  lode  containing  galena  and  stannite.  An  oppor- 
tunity has  been  afforded  by  the  prevalence  of  limestones  in  the  region 
to  study  the  metasomatism  connected  with  cassiterite  veins  in  such 
rocks,  and  the  study  has  shown  that  it  resembles  contact  meta- 
morphism  in  its  dual  aspect — that  is,  metamorphism  both  with  and 
without  addition  of  material. 

a Waller,  G.  A.,  Tin-ore  deposits  of  Mount  Heemskirk,  Govt.  Geol.  Office,  Tasmania, 
1902,  p.  46. 

b Twelvetrees,  W.  H.,  Tin  mines  of  the  Blue  Tier,  Govt.  Geol.  Office,  Tasmania, 
1901,  p.  29. 

c Trustedt,  O.,  Die  Erzlagerstiitten  von  Pitkaranta  am  Ladoga-See  : Bull.  Comm.  Geol.  de. 
Finlande,  No.  19,  1907,  p.  316. 

d Beck,  R.,  Erzlagerstatten,  2d  ed.,  Berlin,  1903,  p.  444. 

54356— Bull.  358—08 5 


66  TIN  DEPOSITS  OF  SEWARD  PENINSULA,  ALASKA. 

In  general,  the  tin  shows  the  intimate  association  with  fluorine 
and  boron  observed  in  most  tin  deposits  the  world  over,  an  associa- 
tion that  is  emphasized  by  the  discovery  of  the  new  iron-tin  borates 
as  essential  constituents  of  lime-silicate  contact  rocks  in  the  meta- 
morphic  aureoles  of  granitic  intrusives, 

PRACTICAL  DEDUCTIONS. 

Developments  in  this  region  have  been  sufficient  to  demonstrate, 
at  least,  that  the  granite-limestone  contacts  are  not  favorable  places 
to  hunt  for  commercial  bodies  of  cassiterite  ore.  Although  a great 
variety  of  contact-metamorphic  rocks  have  been  produced  around  the 
peripheries  of  the  granites  only  a few  that  are  stanniferous  were 
found,  and  in  only  one  was  even  a small  amount  of  cassiterite  detected. 
The  bunchy  and  erratic  character  of  contact-metamorphic  ore  bodies 
has  been  repeatedly  emphasized  in  the  preceding  pages,  and  attention 
has  been  drawn  to  the  difficulty  of  mining  such  deposits  occurring 
along  irregular  contact  surfaces.  The  same  drawbacks  pertain  also 
to  tin  ore  found  in  the  tourmalinized  borders  of  the  granite  stocks. 
In  view  of  the  widespread  belief  in  Seward  Peninsula  that  contact 
deposits  are  likely  sources  of  tin  ore,  it  is  worth  while  to  review  here 
what  is  known  of  cassiterite  contact-metamorphic  deposits  in  other 
parts  of  the  world.  There  has  been  an  actual  production  of  tin  from 
two  only — Pitkaranta  in  Finland  and  Schwarzenberg  in  Saxony— 
and  in  amounts  that  are  relatively  small.  The  ore  at  these  localities 
contains  pyroxene  and  other  minerals  common  in  the  Alaskan  contact- 
metamorphic  deposits,  but  the  ore  formation  is  confined  to  certain 
definite  strata  that  were  evidently  favorable  to  the  precipitation 
of  the  cassiterite.  Some  tin  ore  deposits  of  probable  contact-meta- 
morphic origin  have  been  reported  from  the  Stony  Ford  mine  a and 
St.  Dizier  mine * *  & in  Tasmania,  but  they  have  not  entered  the  ranks  of 
large  producers. 

Quartz  porphyry  dikes,  locally  known  as  lodes,  or  even  as  quartz 
veins,  have  been  prospected  to  some  extent,  owing  to  the  fact  that  the 
original  discovery  of  lode  tin  in  Alaska  was  made  on  a mineralized 
and  altered  dike  of  this  character.  The  value  of  any  such  dike  de- 
pends on  the  number  of  cassiterite  stringers  which  it  contains  and  the 
closeness  with  which  they  are  spaced.  Of  itself,  a quartz  porphyry 
dike  has  no  value.  The  unwelcome  fact  should  be  speedily  realized 
that  few  of  these  dikes  hold  out  any  inducements  whatever  as  pros- 
pective tin  producers. 

« Twelvetrees,  W.  H.,  Tin  mines  of  the  Blue  Tier,  Govt.  Geol.  Office,  Tasmania,  1901, 

p.  29. 

6 Waller,  G.  A.,  Tin  ore  deposits  of  Mount  Heemskirk,  Govt.  Geol.  Office,  Tasmania, 
1902,  p.  46. 


PRACTICAL  DEDUCTIONS. 


67 


Most  of  the  developments  throughout  the  region  are  still  in  the 
prospecting  stage,  and  many  of  the  open  cuts  have  not  uncovered 
solid  bed  rock.  Xo  tonnage  of  tin-bearing  rock,  except  at  one  place 
on  Lost  River,  has  yet  been  blocked  out.  Small  holes  in  the  ground, 
which  give  no  clew  to  either  dip,  strike,  or  persistence  of  the  ore  rock, 
are  held  at  enormous  figures.  The  great  need  of  the  country  is  less 
desultory  prospecting.  The  slate  area  deserves  more  careful  exami- 
nation, as  it  is  possible  that  valuable  quartz  veins  may  exist  within  its 
confines.  The  distribution  of  stream  tin  in  Anikovik  River  and  its 
tributaries  proves  that  the  stanniferous  mineralization  is  not  limited 
to  the  region  at  the  head  of  Buck  Creek,  but  is  more  widely  spread 
throughout  the  slate  belt. 

It  is  probable  that  a great  granite  mass,  of  which  the  stocks  at 
Brooks  Mountain,  Tin  Creek,  and  Cape  Mountain  are  protruding 
bosses,  underlies  the  entire  York  region.  As  shown  by  the  prospects 
of  tin,  tungsten,  copper,  lead,  and  zinc,  and  probably  gold,  this 
magma  was  capable  of  effecting  a varied  mineralization.  As  the 
region  becomes  better  known  and  more  thoroughly  prospected,  addi- 
tional discoveries  will  probably  be  made  from  time  to  time. 


INDEX. 


A.  Page. 

Acknowledgments  to  those  aiding 8 

Actinolite-cassiterite  rock,  thin  section  of, 

figure  showing 34 

Alaska  Chief  property,  description  of 58-59 

American  Tin  Mining  Co.,  development  by. . 62 

Amphibole,  occurrence  and  character  of 20 

Anikovik  River,  tin  on 67 

Apatite,  occurrence  and  character  of 23 

Apophysis,  banded,  plate  showing 46 

Arsenopyrite,  occurrence  and  character  of 18 

Axinite,  occurrence  and  character  of 21 

Azurite,  occurrence  and  character  of 19 

B. 

Banded  vein,  plate  showing 46 

Bartels  Tin  Mining  Co.,  developments  by 40 

Basalt  dikes 15 

Bay  Creek,  rocks  near . 13 

Beaumont,  Elie  de,  on  stockscheider 37-38 

Biotite,  occurrence  and  character  of 22 

Boron  minerals,  association  of,  with  tin 16, 66 

occurrence  of 16,41-42 

Brooks , A . H . , discovery oftinby 7 

preface  by 5 

Brooks  Mountain,  description  of 41 

economic  geology  of 42-44 

geology  of 13,41-42,63 

limestone  from,  thin  section  of,  figure 

showing 34 

Buck  Creek,  geology  at 32-33 

tin  ores  at 33-34 

origin  of 34-35 

tin  placers  on 61-62, 63 

C. 

Calcite,  occurrence  and  character  of 19 

California  River,  rocks  at 13 

Cape  Mountain,  description  of. 35 

elevation  of 10 

geology  at 35-38 

map  of 36 

rocks  on 14 

section  of,  figure  showing 37 

tin  ores  at 38-40 

developments  of 40-41 

Carlson  & Goodwin  claim,  developments  on. . 41 

Cassiterite,  character  of 16-19 

discovery  of 7,17,26 

occurrence  of 13, 16, 19, 24, 33-34, 38-40, 64-65 

thin  section  of,  figure  showing 54 

See  also  Tin. 

Cassiterite  Creek,  fossils  on 13 

geology  on 44 

limestone  on,  view  of 12 

region  of,  map  of 45 

tin  on 44,49 


Page. 

Cassiterite  lode,  description  of 49-50 

developments  on 52 

Cassiterite-quartz  veins,  occurrence  and  char- 
acter of 55 

Cerusite,  occurrence  and  character  of 19 

Chalcopyrite,  occurrence  and  character  of 17 

Chlorite,  occurrence  and  character  of 22 

Chondrodite,  occurrence  and  character  of 21 

Collier,  A.  J.,  on  Mississippian  limestone 14 

on  Port  Clarence  limestone 12, 13 

on  tin  ores 7-8,49,63 

Contact-metamorphi  c rocks,  tin  in 29 

See  also  Metamorphism. 

Cornwall,  stannite  in 16 

D. 

Danburite.  occurrence  and  character  of 21 

Daubree,  A. , on  origin  of  tin 60-61, 64 

Deville  & Caron,  experiments  of 61 

Dikes,  occurrence  and  character  of. . 29, 32-33, 49-51 

Dolcoath  lode,  analysis  of 52 

description  of 51-52, 56, 61 

developments  on 52 

Dolomite,  occurrence  and  character  of 19 

Drainage,  data  on 9-10 

E. 

Ear  Mountain,  description  of 25-26 

geology  of 26-29, 63, 64 

map  of 27 

minerals  of 30 

sections  of,  figures  showing 27, 30 

tin  ores  at,  occurrence  and  character  of.  30-32, 64 

Eldorado  Creek,  tin  on 26 

England,  cassiterite  in 64 

Epidote,  occurrence  and  character  of 21 


Eunson’s  shaft,  section  at,  figure  showing 30 

F. 


Fairhaven  district,  tin  placers  on 63 

Feldspar,  occurrence  and  character  of 20 

Field  work,  scope  of 8 

Finland,  cassiterite  in 65, 66 

Fluorite,  occurrence  and  character  of 18 

relation  of,  to  tin 60-61,66 

Fluorite-silicate  rock,  production  of,  plate 

showing 50 

G. 

Galena,  occurrence  and  character  of 42-44 

Garnet,  occurrence  and  character  of 20 

Geography,  outline  of 9-10 

Geology , description  of 10-15 

Geology,  economic,  description  of  24 

Gold,  occurrence  of 16-17, 33 


69 


70 


INDEX. 


Page, 


Granite,  association  of,  with  tin 16, 24-25 

occurrence  and  character  of 15, 

26-28, 35-36, 41-42, 63, 67 

Gravels,  character  and  distribution  of 15 

gold  and  tin  in 15 

Greenstones,  occurrence  and  character  of 15 

G rouse  Creek,  tin  placers  in 62 

H. 

Hematite,  occurrence  and  character  of 18 

Hess,  F . L.,  on  tin 8 

Hot  Springs  area,  tin  of 63 

Hulsite,  occurrence  and  character  of 23 

Humboldt  Creek,  tin  on 63 

I. 

Ida  B ell  lode,  description  of 50 

Idaho  claim,  description  of 59-60 

Igneous  rocks,  occurrence  and  character  of.  15, 63-64 
Ilmenite,  occurrence  and  character  of 18 

J. 

Tupiter  claim,  developments  on 52 

K. 

Kanauguk  River,  rocks  on 13 

Kaolin,  occurrence  and  character  of 22 

Knopf,  A dol  ph , assignment  of 5, 8 

Kougarok  River,  tin  on 63 

L 

Lagoon  Creek,  section  of,  figure  showing 37 

Ledoux  & Co.,  assay  by 44 

Limestone,  belt  of,  description  of 13-15 

seaming  of,  plates  showing 50, 54 

thin  section  of,  figure  showing 34 

Limonite,  occurrence  and  character  of 19 

Lindgren,  W.,  on  contact  metamorphism 57 

Lost  River,  description  of 44 

Lost  River  region,  cassiterite  veins  of  49-52,55-56 

description  of 44 

geology  of 12-13,44-49 

limestone  of,  veins  in 52-55 

map  of 45 

metamorphism  in 56-57 

tin  ores  in 49-52,67 

developments  of 52-56 

wolframite  veins  o{^ 55-56,57-58 

Ludwigite,  occurrence  and  character  of 23 

M. 

Magnetite,  occurrence  and  character  of 18-19 

Map,  geologic,  of  Cape  Mountain 36 

of  E ar  Mountain 27 

of  Seward  Peninsula 11 

Marble,  orbules  in,  plate  showing 46 

Metamorphism,  occurrence  and  character  of.  14, 16, 
24-25, 28-29, 36-38, 45-49, 56-57, 63-64, 65 
Minerals,  occurrence  and  character  of. . 16-24,29,63 

Molybdenite,  occurrence  and  character  of 17 

Muscovite,  occurrence  and  character  of 22 

N. 

New  South  Wales,  stannite  in 16 

Nickel,  prospects  for 43 

North  Star  Claim,  developments  on 40-41 


O.  Page. 

Olivine,  occurrence  and  character  of 20 

Orbicular  contact  metamorphism,  occurrence 

and  character  of 45-49,63-64 

plate  showing 44 

Orbules,  origin  of,  plate  showing 46 

plate  showing 44 

supply  duct  for,  plate  showing 46 

P. 

Paigeite,  analysis  of 23 

occurrence  and  character  of 23,64 

section  of,  figure  showing 12 

Palazruk,  limestone  near,  description  of 13-15 

Peluk  Creek,  tin  on 33-34 

Phlogopite,  occurrence  and  character  of 14,22 

Port  Clarence  limestone,  character  and  distri- 
bution of 12-13,63 

view  of 12 

Potato  Mountain,  geology  at  and  near 32-33 

Production,  statistics  of 8 

Prospecting,  caution  concerning 30 

status  of 9 

Pyrite,  occurrence  and  character  of 18 

Pyrolusite,  occurrence  and  character  of 19 

Pyroxene,  occurrence  and  character  of 20 

Pyrrhotite,  occurrence  and  character  of 17 

Q. 

Quartz,  occurrence  and  character  of 18 

Quartz-augite  porphyry,  occurrence  and  char- 
acter of 29 

Quartz  Creek,  geology  on 28 

Quartz  porphyry,  occurrence  and  character 

of 32-33 

tin  in 33-34,66 

R. 

Rapid  River,  tin  on 58-59 

Rosenbusch,  H.,  on  contact  metamorphism.  57 
Rutile,  occurrence  and  character  of 19 

S. 

Saxony,  cassiterite  in 65,66 

Scapolite,  occurrence  and  character  of 20 

Schaller,  W.  T.,  analyses  by 23,52,54,58 

Scheelite,  occurrence  and  character  of 24 

Scope  of  work 5 

Seward  Peninsula,  geologic  map  of 11 

Skookum  Creek,  tin  on 62 

Slates,  character  and  distribution  of 10-12 

Smith,  E.  F.,  analyses  by 52 

Sphalerite,  occurrence  and  character  of 17 

Spinel,  occurrence  and  character  of 18 

Stannite,  occurrence  and  character  of 16, 

18,24,57-58 

Sterling  Creek,  tin  and  gold  on 62 

Stibnite,  occurrence  and  character  of 17 

Sullivan,  E.  C.,  homfels  tested  by 38 

Surficial  deposits,  character  and  distribution 

of 15 

Sutter  Creek,  geology  on 32 

tin  placers  on 61,62 

T. 

Tasmania,  cassiterite  in 65 

stannite  in 16 


INDEX. 


71 


Page.  1 

Teller  Mission,  rocks  at 13 

Tin,  association  of,  with  granite 16,24-25  j 

contact  metamorphic  deposits  of 29-30,  | 

38-40,56,66  [ 

patchy  character  of 30, 66  j 

discovery  of 7 

lodes  of,  description  of 25-61 

See  also  Ear  Mountain;  Buck  Creek; 

Cape  Mountain;  Lost  River. 

minerals  of 16 

occurrence  of,  descriptions  of 24-63 

resume  and  conclusions  on 63-66 

ores  of,  origin  of 60-61 

placers  of 24,61-63 

production  of 8 

prospecting  for 9 

See  also  Cassiterite. 

Tin  City,  geology  near 14 

Tin  Creek,  apophysis  on,  plate  showing 46 

geology  on 44, 45-46 

metamorphism  on 45-49, 63-64 

minerals  on 47 

tin  ores  on 49,59-60 

Tin  region,  maps  of  8, 11 

Topaz,  occurrence  and  character  of 21 

Topography,  character  of 9-10 

Tourmaline,  occurrence  and  character  of 21-22 

Trustedt,  O.,  on  orbicular  metamorphism. . . 47 

Tungsten,  occurrence  of 38 

Tuttle  Creek,  geology  on 28 

tin  on 31 


U.  Page. 

United  States  Alaska  Tin  Co.,  developments 

by.  40 

V. 

Veinlets,  occurrence  and  character  of 52-55 

Vesuvianite,  occurrence  and  character  of 21, 

42-43, 47 

Village  Creek,  geology  on  35.41 

Vogt,  J.  H.  L.,  on  origin  of  tin .. 61 

W. 

Wolframite,  occurrence  and  character  of 24 

Wolframite-quartz  veins,  occurrence  and 

character  of 55-56 

wall  rock  adjoining,  plate  showing 56 

Wolframite-topaz  lode,  occurrence  and  char- 
acter of 57-58 

topaz  from,  analysis  of 58 

Wollastonite,  occurrence  and  character  of 20 

Y. 

York,  slates  near,  description  of 10-12 

York  Mountains,  rocks  at 13 

Z. 

Zinc  blende,  occurrence  and  character  of 42 

Zinnwaldite,  analysis  of 54 

occurrence  and  character  of 22, 53-54 

Zircon,  occurrence  and  character  of 21 

Zoisite,  occurrence  and  character  of 21 


o 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  Director 


Bulletin  859 


MAGNETITE  DEPOSITS  OF  THE 
CORNWALL  TYPE 


IN 


PENNSYLVANIA 


BY 

ARTHUR  C.  SPENCER 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1908 


CONTENTS. 


Page. 

Introduction  7 

Geology  of  eastern  Pennsylvania 7 

General  statement 7 

Sedimentary  rocks 8 

Igneous  rocks 9 

General  description  of  ore  deposits 10 

Composition  of  the  ores 11 

Distribution  of  the  ores 12 

Geologic  relations  of  the  ores 12 

Origin  of  the  ores 13 

Replacements  13 

Source  of  the  iron 13 

Differential  metamorphism 16 

Practical  conclusions 16 

Cornwall  and  vicinity 17 

Cornwall  deposits 17 

Distribution  and  surface  relations 17 

Diabase  intrusions c 19 

Structure  of  the  beds 20 

Extent  of  the  deposits 21 

General  statement 21 

The  Cornwall  ore  body 22 

Near-by  deposits 23 

Mines  west  of  Cornwall 28 

Carper  deposit . 28 

Hummelstown  deposits 29 

Berks  County  deposits 29 

Wheatfleld  group 29 

General  description 29 

Diabase  intrusion 30 

Character  of  the  ores 31 

Structure  of  the  rocks 31 

Practical  conclusions 34 

Raudenbusch  mine. 36 

Fritz  Island  and  vicinity 38 

Island  mine 38 

East  bank  of  Schuylkill  River 40 

West  bank  of  Schuylkill  River 41 

Esterly  mine 41 

Boyertown  deposits 43 

General  description 43 

Geology  of  the  district 44 

The  workings 47 

Descriptions  by  Willis 47 


3 


4 


CONTENTS. 


Berks  County  deposits — Continued.  Page. 

Boyertown  deposits — Continued. 

The  workings — Continued. 

Descriptions  by  DTnvilliers 49 

Phoenix  upper  and  middle  slopes 49 

' Phoenix  lower  slope,  or  California  mine 50 

Warwick  mine 51 

Gabel  mine 53 

Later  developments ' 55 

Practical  conclusions 57 

Deposits  southwest  of  Boyertown 61 

Deposits  north  of  Boyertown I 63 

Jones  mine 65 

Warwick  mine 69 

York  County  deposits 1 71 

General  statement 71 

Dillsburg  mines 74 

Introduction  74 

Description  of  mines 75 

Logan  mine 75 

Cox  mine 76 

Price  mine 77 

Grove  mine 77 

Prospects  near  Price  farmhouse 77 

Bell  mine 78 

King  and  Jauss  mines 79 

Altland  mine 81 

Smyser  mine 82 

Underwood  workings 83 

Longnecker  mine . 86 

McCormick  mines.. 88 

Diabase  intrusions  west  of  the  mines 92 

Practical  conclusions 93 

Grantham  mines 96 

Mines  southwest  of  Wellsville 98 

Bender  mine 100 

Index  101 


ILLUSTRATIONS. 


Page. 

Plate  I.  Map  of  the  Mesozoic  belt  in  Pennsylvania 8 

II.  Geologic  sketch  map,  vicinity  of  Cornwall 18 

III.  Structure  sections,  vicinity  of  Cornwall 20 

IV.  Geologic  map,  Cornwall  mines_ 20 

V.  Geologic  sketch  map,  district  south  of  Reading 30 

VI.  Geologic  sketch  map,  vicinity  of  Wheatfield  mines 32 

VII.  Map  of  Fritz  Island  mines 38 

VIII.  Surface  map  of  Boyertown  mines,  showing  position  of  ore 

bodies  at  400  feet  depth 44 

IX.  Geologic  sketch  map,  vicinity  of  Boyertown 44 

X.  General  plan  of  workings,  Boyertown  mines 46 

XI.  Cross  section  at  Boyertown  mines  (along  line  A-B,  PI.  X) 46 

XII.  Cross  section  at  Boyertown  mines  (along  line  C-D , PI.  X) 48 

XIII.  Cross  section  at  Boyertown  mines  (along  line  E-F,  PI.  X) 50 

XIV.  Cross  section  at  Boyertown  mines  (along  line  G-H,  PI.  X) 52 

XV.  Cross  section  at  Boyertown  mines  (along  line  K-L,  PI.  X) 54 

XVI.  Plan  showing  position  of  fault,  California  and  Warwick  mines, 

Boyertown  56 

XVII.  Geologic  sketch  map,  vicinity  of  Jones  and  Warwick  mines 66 

XVIII.  Topographic  map  of  vicinity  of  Jones  and  Kinney  mines 68 

XIX.  Geologic  sketch  map  of  Mesozoic  area  near  Dillsburg 72 

XX.  Geologic  and  topographic  map  of  Dillsburg  iron-ore  fields 74 

Fig.  1.  North-south  structure  section  400  feet  east  of  Ruth  mine,  Wheat- 

field  group 31 

2.  North-south  structure  section  near  slope  No.  1,  Wheatfield  group.  32 

3.  East-west  structure  section,  Wheatfield  group 33 

4.  Sketch  section  at  north  end  of  Fritz  Island 39 

5.  Sketch  section  along  river  bank  east  of  Fritz  Island  mines 39 

6.  Plan  of  upper  level  of  Warwick  mine,  Boyertown 48 

7.  Sketch  showing  possible  structure  between  Hagy  and  Eastern 

veins 59 

8.  Sketch  section  illustrating  relations  of  Black  vein  and  diabase 

sill GO 

9.  Geologic  sketch  map  of  vicinity  of  Boyertown 61 

10.  Geologic  sketch  map  of  region  northeast  of  Boyertown 63 

11.  East-west  structure  section,  Jones  mine 66 

12.  North-south  structure  section,  Jones  and  Kinney  mines 67 

13.  East-west  structure  section,  Kinney  mine 68 

14.  Structure  section,  Warwick  mine 69 

15.  Plan  and  sections  of  Bell  mine 78 

16.  Surface  plan  showing  probable  structure  at  Bell  mine 79 

17.  Survey  of  workings,  Jauss  mine 79 

18.  General  structure  section,  Jauss  mine SO 

19.  Map  of  Underwood  and  Longnecker  mines,  showing  probable 

trend  of  ore  bed 85 

20.  Plan  and  section  of  Longnecker  mine 87 

21.  Sketch  map  showing  situation  of  pits  and  test  holes  on  Mc- 

Cormick tract 90 

5 


MAGNETITE  DEPOSITS  OF  THE  CORNWALL  TYPE 
IN  PENNSYLVANIA. 


By  Arthur  C.  Spencer. 


INTRODUCTION. 

The  deposits  of  iron  ore  which  form  the  subject  of  the  present  re- 
port occur  near  the  edges  of  the  belt  of  Mesozoic  rocks  which  enters 
Pennsylvania  along  Delaware  River  above  Trenton,  N.  J.,  and  ex- 
tends across  the  State  in  a general  southwesterly  direction  to  the 
Maryland  line.  Though  the  deposits  have  been  described  by  several 
geologists  the  present  study  was  undertaken  in  the  belief  that  an  in- 
vestigation of  somewhat  broader  scope  than  any  of  those  previously 
attempted  might  lead  to  an  understanding  of  the  manner  in  which 
the  ores  were  formed,  and  that  a knowledge  of  their  genesis  might 
warrant  practical  suggestions  looking  to  the  discovery  of  ore  bodies 
as  yet  unknown.  The  work  has  been  somewhat  disappointing,  be- 
cause the  observed  facts  do  not  establish  a complete  theory  regarding 
the  origin  of  the  ores,  but  from  a practical  standpoint  the  results 
are  thought  to  be  of  value. 

The  older  descriptions  deal  mainly  with  those  relations  of  the  ore 
bodies  exhibited  in  the  mines  or  pits  from  which  ore  was  being  ex- 
tracted, but  the  deposits  are  here  considered  in  the  light  of  their 
geologic  setting.  The  writer  has  used  much  of  the  information  re- 
corded by  earlier  geologists  and  has  quoted  some  of  their  statements, 
to  which  many  of  his  own  observations  are  merely  supplementary. 
The  field  work  was  done  during  the  autumn  of  1906  and  the  summer 
of  190T. 


GEOLOGY  OF  EASTERN  PENNSYLYANU. 

GENERAL  STATEMENT. 

The  rocks  of  Pennsylvania,  as  recognized  by  the  first  State  geolo- 
gist, TI.  D.  Rogers,  fall  naturally  into  three  main  divisions — the 
pre-Cambrian  gneisses,  schists,  and  volcanic  rocks;  the  Paleozoic 
stratified  formations;  and  the  Mesozoic  stratified  formations  with 

7 


8 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


associated  igneous  rocks.  All  these  divisions  are  represented  in  the 
southeastern  portion  of  the  State,  in  the  region  covered  by  Franklin, 
Adams,  York,  Chester,  Lancaster,  Dauphin,  Lebanon,  Berks,  Mont- 
gomery, Delaware,  Philadelphia,  Bucks,  and  Lehigh  counties,  though 
the  pre-Cambrian  and  Mesozoic  rocks  are  confined  to  the  region  which 
lies  southeast  of  the  Allegheny  Mountain  front  and.  to  the  limestone 
valley  which  trends  from  southwest  to  northeast  through  Cumber- 
land, Dauphin,  Lebanon,  Berks,  and  Lehigh  counties. 

By  folding  and  faulting  the  original  surface  between  the  ancient 
crystalline  rocks  and  the  lowest  Paleozoic  beds  has  been  complexly 
contorted  and  broken,  so  that  great  masses  of  the  Paleozoic  forma- 
tions are  downset  into  the  basement  rocks.  In  four  districts  deep 
erosion  of  relatively  upthrown  blocks  has  revealed  the  pre-Cambrian 
formation.  In  Franklin  and  Adams  counties  the  pre-Cambrian 
rocks  of  South  Mountain  are  largely  of  volcanic  origin.  They  are 
here  intricately  infolded  with  Paleozoic  quartzites  and  limestone. 
In  the  vicinity  of  Philadelphia  and  southwestward  from  that  city  the 
pre-Cambrian  rocks  include  schists  and  massive  igneous  intrusions. 
In  northern  Chester  County  and  in  Berks  and  Lehigh  counties  they 
are  mainly  granular  gneisses. 

SEDIMENTARY  ROCKS. 

Of  the  many  iormations  which  are  comprised  in  the  whole  of  the 
Pennsylvania  Paleozoic  section  only  the  Cambrian  quartzites,  the 
Cambro-Ordovician  limestones,  and  the  Ordovician  shales  occur  in 
the  region  here  under  discussion.  In  the  following  pages  these  divi- 
sions of  the  Paleozoic  sequence  are  designated  as  “ No.  I ” sandstone, 
“ No.  II  ” limestone,  and  “ No.  Ill  ” shale,  in  accordance  with  the 
usage  of  the  Second  Geological  Survey  of  Pennsylvania.  Taken 
together,  formations  46 1 ” to  u III  ” extend  over  a belt  of  country  from 
10  to  20  miles  wide,  lying  southeast  of  the  Allegheny  Front.  The 
limestone,  being  relatively  much  thicker  than  the  sandstone,  is  the 
more  prominent  of  the  two,  while,  as  the  uppermost  of  the  three  mem- 
bers, the  shale  has  been  more  extensively  removed  by  erosion  than  the 
limestone  and  sandstone. 

The  Mesozoic  strata,  made  up  principally  of  coarse-grained  red 
sandstone  and  red  shale,  are  distributed  in  a belt  from  8 to  12  miles 
wide,  extending  from  Delaware  Fiver  in  a southwesterly  direction 
to  the  Schuylkill,  thence  westward  to  the  Susquehanna,  and  from 
the  Susquehanna  again  southwestward  to  the  boundary  between 
Pennsylvania  and  Maryland.  Locally,  heavy  beds  of  limestone  con- 
glomerate are  present. 

Though  these  red  formations  are  now  commonly  designated  the 
Newark  group,  they  are  here  called  simply  Mesozoic,  the  term  being 


MAP  OF  THE  MESOZOIC  BELT  IN  PENNSYLVANIA,  SHOWING  PRINCIPAL  INTRUSIONS  OF  DIABASE. 
Data  in  part  from  Second  Geological  Survey  of  Pennsylvania. 


GEOLOGY  OF  EASTERN  PENNSYLVANIA. 


9 


consistent  with  Paleozoic,  which  it  has  been  found  convenient  to 
emplo}^  in  the  descriptions  that  follow.  Considered  in  reference  to 
other  stratified  Mesozoic  formations  which  overlap  the  Newark  rocks . 
in  eastern  New  Jersey,  the  latter  are  properly  designated  as  lower 
Mesozoic,  but  failure  thus  to  particularize  their  position  in  the  strati- 
graphic column  leads  to  no  confusion  in  discussing  the  geology  of 
Pennsylvania. 

The  belt  of  Mesozoic  rocks  in  eastern  Pennsylvania  is  part  of  an 
unbroken  curving  zone  about  300  miles  in  length,  extending  from  the 
west  shore  of  Hudson  River  across  New  Jersey,  Pennsylvania,  and 
Maryland,  and  into  Virginia  as  far  as  Culpeper  County.  Several 
outliers  in  the  continuation  of  the  general  course  of  this  belt  are 
found  in  southern  Virginia  and  in  North  Carolina,  while  northward 
from  Hudson  River  there  is  an  extensive  basin  of  corresponding 
rocks  in  the  valley  of  Connecticut  River,  and  another  bordering  the 
southeast  side  of  the  Bay  of  Fundy  in  Nova  Scotia. 

In  Pennsylvania  the  Mesozoic  strata  wTere  deposited  upon  a pre- 
viously eroded  surface  on  which  were  exposed  all  the  older  rocks  now 
represented  in  the  region.  In  places  along  the  borders  of  the  Meso- 
zoic belt  pre- Cambrian  gneisses  are  present.  Elsewhere  “ No.  I ” 
sandstone  or  “ No.  Ill  ” shale  is  overlapped  by  the  Mesozoic  strata, 
but  on  the  whole  “ No.  II  ” limestone  forms  the  usual  basement. 
Bowlders  entering  into  the  make-up  of  the  limestone  conglomerates 
that  occur  in  places  along  the  edge  of  the  belt  have  evidently  been 
derived  from  the  formation  last  mentioned. 

IGNEOUS  ROCKS. 

The  zone  comprising  the  various  Mesozoic  basins  is  characterized 
by  intrusions  of  diabase  or  surface  flows  of  basalt,  both  of  which  are 
commonly  called  trap  rock,  or  simply  trap  (PI.  I).  The  diabase 
dikes  occur  in  the  districts  between  the  several  basins,  and  southward 
along  the  general  trend  of  the  zone  they  persist  across  South  Carolina 
and  well  into  Alabama.  Although  the  strip  of  country  in  which  the 
dikes  are  present  is  considerably  wider  than  any  of  the  separate  belts 
of  Mesozoic  strata,  the  great  bulk  of  the  igneous  material  is  associated 
with  the  Mesozoic  rocks.  In  New  England  and  New  Jersey  both 
extensive  surface  flows  and  invading  masses  are  present,  but  in  Penn- 
sylvania nearly  all  of  the  igneous  rock  is  distinctly  intrusive.  The 
intrusions  are  mainly  sills  which  follow  the  bedding  of  the  invaded 
formations  more  or  less  closely,  but  local  and  even  extensive  cross- 
cutting may  be  observed. 

As  the  igneous  material  could  not  have  originated  either  within 
the  mass  of  the  Mesozoic  sediments  or  within  the  underlying  Paleozoic 
formations,  a deep-seated  source  must  be  admitted.  In  order  to  have 


10 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


reached  the  positions  which  it  now  occupies  the  diabase  must  have 
come  up  through  channels  traversing  the  lower  Mesozoic  strata  and 
the  basement  rocks  beneath  them.  Presumably  the  ordinarily  nar- 
row dikes  that  occur  outside  of  the  Mesozoic  belt  were  feeders  for 
intrusive  sills  and  for  surface  flows  associated  with  portions  of  the 
Mesozoic  sediments  which  have  been  removed  by  erosion.  If  this  be 
true  the  feeders  of  the  sills  that  still  remain  are  perhaps  for  the  most 
part  similar  narrow  dikes. 

The  ore  deposits  described  in  the  following  pages  are  intimately 
associated  with  intrusive  masses  of  diabase  and  most  of  them  are 
contained  in  calcareous  strata,  either  in  the  limy  rocks  belonging  to 
Paleozoic  “ No.  II  ” limestone,  outcropping  near  the  edge  of  the  Meso- 
zoic belt,  or  in  the  beds  of  limestone  conglomerate  that  locally  mark 
the  base  of  the  Mesozoic  section.  Since  the  deposits  are  situated  in 
each  case  near  the  surface  of  unconformity  between  the  Mesozoic  and 
the  underlying  Paleozoic  formations,  there  is  reason  to  believe  that  the 
diabase  masses  associated  with  the  ores  are  bodies  which  cut  across 
the  Paleozoic  basement  rocks.  These  masses  are  of  considerable  size. 
Some  of  them  were  evidently  the  feeders  of  sills  which  penetrate  the 
Mesozoic  strata. 

GENERAL  DESCRIPTION  OF  ORE  DEPOSITS. 

The  Cornwall  type  of  iron  ore  is  so  called  from  the  important  Corn- 
wall mine  in  Lebanon  County,  Pa.  The  ores  are  essentially  magne- 
tite, but  they  contain  pyrite^in  amounts  which  make  it  necessary  to 
roast  them  before  they  can  be  used  in  the  blast  furnace.  Some 
specular  hematite  occurs  in  certain  of  the  mines,  but  the  amount  of 
this  mineral  is  relatively  unimportant. 

The  ore  occurs  in  large  and  small  masses  of  varying  form,  either 
entirely  inclosed  by  stratified  sedimentary  rocks  or  lying  in  such  rocks 
where  they  come  in  contact  with  masses  of  intrusive  diabase.  The 
ore  minerals  appear  to  have  been  formed  by  more  or  less  complete 
chemical  substitution  in  the  body  of  the  rock,  the  portion  of 
the  rock  not  replaced  constituting  the  principal  gangue  of  the  ore. 
Aside  from  the  deposition  of  the  iron  minerals  the  limy  strata  asso- 
ciated with  the  ore  bodies  show  remarkably  little  metamorphism,  and 
though  a few  characteristic  minerals  of  contact  metamorphism  occur 
they  are  so  uncommon  as  to  almost  escape  observation.  The  Corn- 
wall mines  haye  yielded  more  than  20,000,000  tons  of  ore,  from  what 
is  essentially  a single  great  ore  body,  though  it  contains  extensive 
partings  of  barren  rock.  The  other  deposits  are  all  much  smaller, 
though  several  of  them  are  still  of  important  size. 


GENERAL  DESCRIPTION. 


11 


COMPOSITION  OF  THE  ORES. 

The  iron  content  of  these  ores  is  extremely  variable,  but  as  the  ore 
is  mined  probably  averages  not  far  from  45  per  cent.  Rather  con- 
stant chemical  characteristics  are  low  phosphorus,  high  sulphur,  silica, 
lime,  and  magnesia,  and  the  presence  of  copper.  Small  amounts  of 
cobalt  have  been  found  in  ores  from  Cornwall  and  Dillsburg.  Many 
analyses  of  ore  from  the  different  mines  may  be  found  in  the  reports 
of  the  Pennsylvania  Geological  Survey,  from  which  the  following 
are  extracted : 

Partial  analyses  of  Cornwall  ore. 


[A.  S.  McCreath,  analyst.] 


1.  2. 

3. 

4. 

Metallic  iron 

G4.900  51.450 

48.  800 

41. 900 

Metallic  manganese 

.158  .072 

.057 

.194 

Metallic  copper 

. 005  . 559 

.599 

.319 

Alumina 

.324  1.080 

2.315 

4.970 

Lime 

1.010  1 2.600 

4.  330 

2.810 

Magnesia 

1.131  | 6.652 

5.  531 

7.  457 

Sulphur 

. 071  2. 459 

1.807 

.428 

Phosphorus 

.014  .010 

.018 

.019 

Silica 

3.980  12.270 

12. 940 

20.  910 

Phosphorus  in  100  parts  iron 

.021  1 .019 

0.036 

.045 

“ Lesley,  J.  P.,  and  D’Invilliers,  E.  V.,  Cornwall  iron  ore  mines : Ann.  Kept.  Second 
Geol.  Survey  Pennsylvania  for  1885,  1886,  pp.  532,  533. 


1.  Analysis  of  115  pieces  of  niggerhead  ore  from  Middle  Hill. 

2.  Analysis  of  fine  or  soft  No.  3 ore  from  west  cut,  north  side,  Middle  Hill. 

3.  Analysis  of  “ No.  1 ore  ” from  east  face,  Middle  Hill. 

4.  Analysis  cf  “ No.  1 light  ore  ” from  west  cut,  south  face,  Middle  Hill. 
All  the  above  were  dried  at  212  + ° F.  before  analysis. 


Partial  analyses  of  ores  from  Berks  and  York  counties ,a 


1. 

2. 

3. 

4. 

5. 

6. 

Iron 

43.  40 

43. 00 

42.75 

39.  60 

38.05 

34.55 

21.21 

Silica 

11. 13 

14. 02 

22. 10 

20.  20 

16. 13 

Alumina,  lime,  and  magnesia 

18.90 

13.  86 

11.45 

19. 18 

19.  77 

22. 38 
.17 

Copper 

.01 

.59 

. 12 

.56 

Manganese . 

.01 

.23 

1.94 

.42 

21 

Sulphur 

.43 

.53 
. 02 

.59 

1.14 

.04 

1.64 

.03 

Phosphorus 

.09 

.01 

.06 

a Lesley,  J.  P.,  and  D'lnvilliers,  E.  V.,  op.  cit.,  p.  537. 


1.  Black  ore,  163  pieces,  from  Warwick  mine,  Boyertown,  Berks  County,  A.  S. 
McCreath. 

2.  Magnetic  ore  from  Island  mine,  Reading,  slope  No.  1.  Leonard  Peckitt,  Reading. 

3.  Dillsburg  ore  from  A.  Underwood's  mine,  A.  S.  McCreath. 

4.  Magnetic  ore  from  Wheatfield  mine,  Berks  County. 

5.  Magnetic  ore,  25  pounds,  from  Island  mine,  Reading,  A.  S.  McCreath. 

6.  “ Blue  ore,”  20  pounds,  from  Phoenix  mines,  Boyertown,  A.  S.  McCreath. 

Workings  at  the  surface  formerly  furnished  soft  ore  free  from  sul- 
phur, but  this  material  gives  place  to  hard  sulphurous  ore  at  rela- 
tively shallow  depths. 


12 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


DISTRIBUTION  OF  THE  ORES. 

So  far  as  known,  ores  of  the  Cornwall  type  do  not  occur  outside 
of  Pennsylvania,  though  certain  small  veins  of  magnetite  occurring 
in  masses  of  intrusive  diabase  in  Nova  Scotia  may  be  more  or  less 
closely  related  to  them.  In  Pennsylvania  the  ores  haiTe  been  mined 
on  a considerable  scale  at  five  localities  in  Berks  County, • namely : At 
Boyertown;  at  two  places  south  of  Reading;  7 miles  southwest  of 
Reading,  near  Fritztown;  and  near  Joanna  station,  21  miles  northeast 
of  Morgantown.  In  Chester  County  they  were  formerly  mined  at 
Warwick,  though  this  deposit  is  entirely  exhausted.  The  great  Corn- 
wall mines  are  situated  in  Lebanon  County,  and  near  them  are  two 
other  small  deposits.  In  York  County  a large  number  of  operations 
have  been  carried  on  in  the  vicinity  of  Dillsburg.  Of  all  the  deposits 
which  have  been  mentioned  only  the  one  at  Cornwall  is  now  worked 
in  a large  way,  though  the  several  interests  which  formerly  controlled 
the  Boyertown  properties  have  recently  been  consolidated  so  that  these 
mines  may  be  started  at  an  early  date.  At  Dillsburg  some  ore  was 
mined  in  1903,  and  surface  mining  on  a small  scale  was  in  progress 
at  the  Wheatfield  group  in  1906;  the  other  mines  have  been  aban- 
doned for  many  years. 

GEOLOGIC  RELATIONS  OF  THE  ORES. 

Though  in  the  past  there  has  been  considerable  discussion  concern- 
ing the  stratigraphic  position  of  the  deposits,  it  is  now  agreed  that 
in  York  County  they  lie  in  Mesozoic  strata  and  in  most  of  the  other 
localities  in  limestones  or  limy  shales  of  Paleozoic  age.® 

The  Cornwall  deposit  is  situated  at  the  top  of  “ No.  II  ” limestone 
of  the  Pennsylvania  section,  just  under  the  “ No.  Ill  ” (“  Hudson  ”) 
shale;  the  Boyertown,  Fritz  Island,  Raudenbusch,  Wheatfield,  and 
Jones  deposits  are  in  strata  which  apparently  belong  near  the  base  of 
“ No.  II  ” limestone.  The  Warwick  deposit  lies  at  the  base  of  Meso- 
zoic beds  that  rest  upon  pre-Cambrian  gneisses. 

It  has  been  found  that  large  masses  of  intrusive  diabase  are  present 
near  each  of  the  existing  ore  bodies  and  usually  in  actual  contact  with 
them.  The  existence  of  diabase  near  the  mines  is  noted  in  every  pub- 
lished description  of  these  magnetite  deposits,  and  the  present 
investigation  has  served  to  emphasize  both  the  size  of  these  igneous 
masses  and  the  importance  of  their  relation  to  the  ore  deposits.  It 
is  thought,  indeed,  that  the  origin  of  the  ores  must  have  been  directly 
connected  with  the  intrusion  of  the  igneous  rocks. 

a Lesley,  .T.  P.,  and  D’Invilliers,  E.  V.,  op.  cit.  Also,  D'Invilliers,  E.  V.,  Iron  ore  mines 
and  limestone  quarries  of  the  Cumberland-Lebanon  Valley : Ann.  Rept.  Second  Geol. 
Survey  Pennsylvania  for  1886,  pt.  4,  1887. 


GENERAL  DESCRIPTION. 


18 

/ 

ORIGIN  OF  THE  ORES. 

REPLACEMENTS. 

If  the  various  deposits  be  considered  together  the  theory  of  origin 
which  seems  to  be  required  by  their  geologic  relations  is  that  the 
magnetite  ore  bodies  of  the  Cornwall  type  have  been  formed  by  the 
more  or  less  complete  metasomatic  replacement  of  sedimentary  rocks 
by  iron  minerals  precipitated  from  heated  solutions  set  into  circu- 
lation by  the  invading  diabase.  The  rocks  which  have  been  thus 
replaced  are  usually  limestones,  limy  shales,  or  limestone  conglom- 
erates. 

Previous  writers,  including  H.  D.  Rogers,  T.  Sterry  Hunt,  Persifor 
Frazer,  jr.,  J.  P.  Lesley,  and  E.  V.  d’lnvilliers,  have  held  that  while 
the  present  magnetic  condition  of  the  ores  might  be  due  to  the  meta- 
morphosing effect  of  the  trap  rocks  (diabase),  the  deposits  had  been 
formed  before  the  introduction  of  these  rocks.a 

Material  from  almost  any  one  of  the  mines  affords  abundant  evi- 
dence that  the  ore  minerals  have  been  deposited  by  substitution  or 
chemical  replacement  of  the  limy  rocks.  Much  of  the  lean  ore  con- 
sists of  alternating  layers  of  the  iron  minerals  and  unaltered  rock, 
showing  definitely  that  certain  portions  of  the  rock  have  been  more 
favorable  for  replacement  than  others.  At  Cornwall  many  examples 
may  be  seen  in  which  thin  layers  of  ore  conforming  to  the  stratifica- 
tion of  the  limy  shales  are  connected  by  cross  seams,  which  show 
beyond  a doubt  that  the  ore  minerals  could  not  have  been  formed 
contemporaneously  with  the  inclosing  rock,  but  that  they  must  have 
been  introduced  subsequently.  It  is  the  writer’s  conception  that  the 
solutions  which  accomplished  the  deposition  of  the  ores  must  have 
been  in  the  condition  of  vapor  when  they  penetrated  the  rocks. 

SOURCE  OF  THE  IRON. 

The  source  of  the  solutions  concerned  in  the  formation  of  the  ores 
and  in  the  general  metamorphism  of  the  rocks  in  the  vicinity  of  the 
igneous  masses  and  the  source  of  the  iron  which  the  deposits  contain 
can  not  be  satisfactorily  determined.  The  observed  facts  lead  to  no 
definite  conclusion  on  either  of  these  points,  though,  all  things  con- 

° Rogers,  H.  D.,  Geology  of  Pennsylvania,  vol.  2,  1858,  pp.  687,  708,  718. 

Hunt,  T.  S.,  The  Cornwall  iron  mine  and  some  related  deposits  in  Pennsylvania  : Trans. 
Am.  Inst.  Min.  Eng.,  vol.  4,  1875,  pp.  508-510.  • 

Frazer,  P.,  jr.,  Second  Geol.  Survey  Pennsylvania,  Rept.  CC,  1877,  pp.  198-400.  Also, 
A study  of  the  specular  and  magnetic  iron  ores  of  the  new  red  sandstone  in  York 
County,  Pa.  : Trans.  Am.  Inst.  Min.  Eng.,  vol.  5,  1877,  pp.  132-143. 

Lesley,  J.  P.,  and  D’lnvilliers,  E.  V.,  Report  on  the  Cornwall  iron-ore  mines,  Lebanon 
County : Ann.  Rept.  Second  Geol.  Survey,  Pennsylvania,  for  1885,  1886,  pp.  491-570 ; 
Final  Rept.  Second  Geol.  Survey  Pennsylvania,  vol.  1,  1892,  pp.  351-357. 

D’lnvilliers,  E.  V.,  The  Cornwall  iron-ore  mines,  Lebanon  County,  Pa. : Trans.  Am. 
Inst.  Min.  Eng,,  vol.  14,  1886,  pp.  473-904. 


14 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


sidered,  if  it  be  admitted  that  the  heat  of  the  intrusive  rocks  was  the 
prime  cause  of  the  circulation  of  the  solutions  which  formed  the  ore 
it  appears  more  likely  that  both  the  waters  and  the  iron  were  fur- 
nished by  the  igneous  rock  than  that  they  could  have  been  derived 
from  an  outside  source.  Possibilities  which  naturally  present  them- 
selves are  as  follows: 

1.  The  water  was  of  meteoric  origin  and  the  iron  came  from  the 
sedimentary  rocks. 

2.  The  water  was  of  juvenile  origin  (that  is,  it  was  expelled  from 
the  igneous  rocks)  and  the  iron  came  from  the  sedimentary  rocks. 

3.  The  water  was  of  juvenile  origin  and  contained  the  iron  in  solu- 
tion when  it  escaped  from  the  igneous  rocks. 

The  suggestion  that  ordinary  ground  waters  could  have  been  heated 
by  the  invading  igneous  rocks  and  thus  have  been  enabled  to  cause 
extensive  induration  of  the  invaded  Mesozoic  strata,  leaching  them  of 
their  contained  iron  and  concentrating  it  into  ore  deposits  occupying 
the  observed  situation,  is  opposed  by  several  considerations.  In  the 
first  place,  it  appears  that  waters  from  any  source  outside  of  the 
igneous  rock,  whatever  their  natural  courses  of  circulation,  if  un- 
affected by  the  intrusive  masses,  could  never  closely  approach  the 
heated  bodies  of  rock,  for  the  reason  that  steam  would  be  generated 
in  the  vicinity  of  the  contacts  and  the  resulting  pressure  would  tend 
to  drive  all  waters  outward  from  the  source  of  heat.  Under  such  con- 
ditions if  ore  deposits  were  formed  they  would  not  be  segregated  at 
the  igneous  contacts,  but  instead  would  be  some  distance  away,  which 
is  contrary  to  the  existing  relations.  A second  argument  against  the 
suggestion  is  that  the  deposits  are  neither  as  numerous  nor  as  widely 
distributed  as  would  be  expected  if  the  iron  had  been  contributed 
by  the  invaded  formations.  The  only  sedimentary  rocks  which  can 
be  considered  as  at  all  competent  to  have  furnished  sufficient  iron  for 
the  known  deposits  are  the  Mesozoic  sandstones  and  shales  that  occur 
in  the  vicinity  of  all  the  deposits,  as  the  Paleozoic  formations  are  made 
up  of  rocks  containing  very  small  amounts  of  iron.  In  so  far  as  they 
have  not  been  altered  by  the  influence  of  the  intrusive  diabases  the 
Mesozoic  rocks  are  of  almost  uniform  appearance  throughout  the 
region  and  from  a few  recorded  analyses  it  may  be  judged  that  they 
^carry  from  5 to  8 per  cent  of  iron  oxide.  Everywhere  in  the  neigh- 
borhood of  the  intrusive  masses  the  sandstone  and  shales  have  been 
extensively  metamorphosed.  In  places  balls  of  epidote  have  been 
formed  in  the  shales ; elsewhere  small  segregations  of  specular  hema- 
tite occur  in  coarse  sandstones;  and  in  conglomerates  some  of  the 
pebbles  are  surrounded  by  rims  of  garnet,  tremolite,  and  hornblende. 
Changes  of  this  sort  characterize  the  more  intense  phases  of  metamor- 
phism and  are  observed  only  near  the  diabase  contacts;  more  exten- 


GENERAL  DESCRIPTION. 


15 


sive  alteration  of  a less  striking  nature  is  manifested  by  a general 
induration  of  the  rock  and  by  a loss  of  the  original  red  color. 

Though  the  general  bleached  condition  of  the  Mesozoic  strata  in  the 
neighborhood  of  the  intrusive  masses  points  to  these  rocks  as  a possi- 
ble source  of  the  segregated  iron,  it  is  not  certain  that  the  whitened 
rocks  have  actually  lost  their  iron,  for  the  original  amount  of  this 
element  may  still  be  present  in  a different  chemical  state.  No  investi- 
gation has  been  made  to  settle  the  question  thus  raised,  but  it  does 
seem  that  if  the  iron  of  the  sandstones  has  been  depleted  in  a few 
places  the  same  thing  must  have  taken  place  generally,  because  the 
appearance  of  the  altered  rocks  is  the  same  in  many  places.  If  the 
known  deposits  of  iron  ore  had  been  formed  from  solutions  of  this 
origin  a certain  amount  of  segregation  should  be  found  in  associa- 
tion with  the  bleached  rocks  wherever  they  occur.  The  fact  that  the 
ore  deposits  are  so  localized  is  thus  against  the  idea  that  the  iron 
which  the}r  contain  has  been  furnished  by  the  sedimentary  rocks. 

The  conclusion  that  the  sedimentary  rocks  are  not  likely  to  have 
furnished  the  iron  applies  as  well  when  the  active  waters  are  regarded 
as  having  come  from  the  igneous  rocks  as  it  does  when  a meteoric 
source  is  assigned  to  them. 

It  can  hardly  be  doubted  that  the  general  alteration  of  the  shales 
and  sandstones  near  the  igneous  rocks  has  resulted  from  the  action 
of  heated  water  and  steam  percolating  through  the  sandstones  and 
shales.  If  the  waters  which  took  part  in  the  metamorphism  had 
come  out  of  the  igneous  rocks,  either  from  the  masses  adjacent  to 
the  altered  sediments  or  from  much  deeper  masses  which  have  not 
been  exposed  to  view,  they  could  hardly  have  made  an  excursion 
through  the  stratified  rocks  and  later  returned  to  the  contact,  as  they 
must  have  done  to  have  deposited  the  ore  bodies  at  Boyertown,  at 
Cornwall,  at  the  J ones  mine,  and  at  the  larger  ore  beds  of  the  Dills- 
burg  field. 

Only  one  of  the  several  adverse  considerations  presented  above 
stands  in  the  way  of  the  suggestion  that  both  the  waters  which  ef- 
fected the  metamorphism  and  the  iron  which  was  deposited  by  these 
waters  were  driven  from  the  igneous  rocks;  namely,  the  uncom- 
monness of  the  deposits.  If  certain  of  the  intrusive  masses  furnished 
iron  for  large  deposits,  why  is  it  that  similar  segregations  do  not 
occur  in  association  with  every  important  mass  of  diabase  ? Though 
the  question  can  not  be  satisfactorily  answered,  our  general  knowl- 
edge concerning  the  occurrence  of  ore  deposits  at  igneous  contacts 
points  to  the  conclusion  that  the  nature  of  the  solutions  given  off  by 
different  parts  of  igneous  rock  masses  is  subject  to  wide  variation, 
so  that  it  is  by  no  means  necessary  to  believe  that  identical  materials 
must  have  been  introduced  everywhere  in  the  vicinity  of  intrusive 


16 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


masses  of  the  diabase,  even  though  the  igneous  rock  be  accepted  as 
the  source  of  the  iron  segregated  locally  at  the  contact  with  the  in- 
vaded strata. 

DIFFERENTIAL  METAMORPHISM. 

Whatever  the  actual  source  of  the  iron  may  have  been,  it  can  not 
be  doubted  that  different  masses  of  diabase  within  the  same  general 
field  may  have  differed  greatly  in  respect  to  efficiency  in  produc- 
ing metamorphism,  but,  other  things  being  equal,  it  can  be  assumed 
that  the  directness  of  the  paths  by  which  the  intrusions  came  into 
their  present  positions  must  have  been  a very  important  factor 
influencing  the  relative  amount  of  alteration  and  mineralization 
which  the  various  masses  of  diabase  were  capable  of  producing.  It 
seems  evident  that  the  transfer  of  heat  and  the  movement  of  mineral- 
izing waters  must  have  continued  for  a much  longer  period  in  the 
vicinity  of  strongly  crosscutting  masses  of  igneous  rock  than  adjacent 
to  others  having  less  direct  connection  with  the  deep-seated  reservoir 
which  supplied  the  molten  rock  material.  This  is  accepted  because 
the  deep  reservoir  is  conceived  to  have  been  the  original  source  of  all 
the  energy  involved  in  the  chemical  reactions  of  metamorphism  and 
ore  deposition. 

PRACTICAL  CONCLUSIONS. 

The  geologic  features  of  the  various  deposits  which  have  been 
studied  are  thought  to  warrant  the  following  general  suggestions 
to  those  who  in  the  future  may  make  practical  explorations  for  new 
ore  bodies  in  this  field. 

1.  Ore  bodies  are  to  be  sought  only  on  or  near  the  walls  of  masses  . 
of  diabase. 

2.  Large  masses  of  diabase  are  more  favorable  for  ore  deposits 
than  smaller  masses. 

3.  Crosscutting  intrusions  and  highly  inclined  sills  are  more  favor- 
’ able  than  sills  of  low  inclination. 

4.  Limestones  and  limy  shales  are  far  more  likely  to  be  replaced 
by  ore  than  clay  shales  or  sandstones. 

5.  Particularly  favorable  locations  for  ore  are  found  in  masses  of 
limestone  that  lie  between  bodies  of  diabase  and  beds  that  are  in  a 
marked  degree  less  susceptible  than  limestone  to  the  metamorphosing 
influence  of  the  igneous  rocks. 

6.  The  most  promising  situations  will  be  found  at  places  where 
the  largest  number  of  the  above-stated  favorable  conditions  occur  in 
combination. 

Many  or  all  of  the  more  favorable  conditions  enumerated  existed 
at  places  where  the  larger  ore  deposits  of  the  Cornwall  type  were 
formed,  and  as  several  of  these  conditions  may  be  fairly  inferred 


CORNWALL  DEPOSITS. 


17 


to  exist  in  a few  other  localities,  usually  in  the  vicinity  of  the  mines 
which  have  been  operated,  still  other  deposits  of  iron  ore  may  yet 
be  found  in  the  same  field.  The  geologic  descriptions  which  follow 
have  been  prepared  with  especial  reference  to  the  possibility  of  indi- 
cating situations  in  which  it  may  prove  worth  while  to  look  for 
deposits  of  iron  ore  as  yet  unrecognized. 

CORNWALL  AND  VICINITY. 

CORNWALL  DEPOSITS. 

DISTRIBUTION  AND  SURFACE  RELATIONS. 

The  Cornwall  ore  banks  are  situated  5 miles  from  Lebanon,  Pa., 
on  the  south  side  of  the  Lebanon  Valley,  along  the  edge  of  which 
Paleozoic  limestones  and  slates  give  place  to  intrusive  diabase  and  to 
conglomerates,  sandstones,  and  shales  of  Mesozoic  age  (PI.  II).  The 
different  formations  have  a general  east-west  trend  through  all  this 
region,  and  for  several  miles  both  east  and  west  of  Cornwall  the  older 
(Paleozoic)  and  newer  (Mesozoic)  formations  are  separated  by  an 
intrusive  mass  of  diabase  which  has  a width  in  outcrop  of  1,400  to 
2,900  feet.  The  mines  lie  just  south  of  this  diabase  in  an  isolated  area 
of  limestone,  the  southern  boundary  of  which  is  formed  by  overlap- 
ping Mesozoic  beds.  Eastward  from  the  ore  hills  for  a distance  of 
somewhat  more  than  a mile  a narrow  strip  of  slaty  rocks  comes  be- 
tween the  diabase  and  the  lowermost  Mesozoic  strata  exposed  in  this 
vicinity.  West  of  the  workings  a narrower  strip  of  the  same  rock  in 
similar  position  outcrops  for  perhaps  1,000  feet.  The  limestones  and 
interlayered  limy  shales  south  of  the  diabase  have  been  more  or  less 
completely  replaced  by  magnetite,  somewhat  contaminated  by  pyrite 
and  chalcopyrite,  and  it  is  these  impregnated  strata  that  constitute  the 
great  deposit  from  which  more  than  21,000,000  tons  of  iron  ore  have 
been  extracted  since  1853. 

The  position  and  surface  relations  of  the  ore-bearing  strata  to  the 
various  rocks  which  have  been  spoken  of  in  the  foregoing  paragraph 
are  clearly  exhibited  on  the  maps  (Pis.  II  and  IV),  and  the  cross- 
sections  (PL  III)  indicate  the  supposed  relations  underground.  These 
sections  are  intended  to  show  the  kind  of  structure  that  seems  to  be 
required  by  the  existing  surface  distribution  of  the  various  kinds  of 
rocks  and  by  their  strikes  and  dips,  in  so  far  as  these  can  be  observed. 
As  guides  the  sections  are  believed  to  be  of  some  value,  but  thicknesses, 
strikes,  and  dips  of  buried  strata  are  manifestly  not  ascertainable 
factors  in  cases  like  the  present,  where  masses  of  intrusive  rock,  and 
in  addition  a great  unconformity  of  deposition,  are  involved  in  the 
structure  to  be  interpreted. 

54370 — Hull.  359— OS 2 


18 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


On  the  surface  the  ore,  together  with  such  masses  of  lean  or  barren 
rock  as  accompany  it,  is  bounded  on  the  west,  north,  and  east  by  dia- 
base, a tongue  of  which  likewise  limits  the  Big  Hill  mine  on  the 
south.  Between  the  tongue  of  diabase  that  forms  the  southern  side  of 
Big  Hill  and  the  first  exposure  of  Mesozoic  beds  in  the  low  ground 
immediately  south  of  Miners  village  the  slope  is  covered  by  loose 
debris,  so  that  it  is  impossible  to  say  what  the  distribution  of  the  vari- 
ous rocks  actually  is.  It  seems  very  likely,  however,  that  some  of  the 
strata  which  are  elsewhere  converted  into  ore  occupy  at  least  a por- 
tion of  this  hidden  ground.  South  of  the  mines  scattered  outcrops 
serve  to  indicate  rather  closely  the  northerly  limit  of  the  Mesozoic 
rocks,  the  lowest  bed  of  which  is  a conglomerate  composed  of  angular 
quartz  fragments  in  a cement  of  bluish  clay.  This  peculiar  rock  has 
been  called  porphyry  by  casual  observers,  but  its  clastic  nature  is 
obvious  on  close  examination.  South  of  the  present  workings  in 
Middle  Hill,  and  for  some  distance  toward  the  west,  loose  debris  de- 
rived from  the  near-by  hill  covers  the  edge  of  the  ore,  but  the  blue 
conglomerate  has  been  revealed  in  a reservoir  excavation  near  the 
Mount  Hope  road,  and  this  rock  probably  constitutes  the  immediate 
capping  of  the  ore-bearing  strata  from  this  place  eastward  to  the 
exposures  along  the  railroad  track  just  below  the  superintendent’s 
office.  West  of  the  Mount  Hope  road  the  same  rock  may  be  followed 
for  some  distance,  but  in  this  direction  its  outcrop  approaches  the 
diabase,  and  the  rock  is  considerably  baked  and  indurated.  On  the 
little  knoll  just  west  of  the  road  a narrow  strip  of  slate  is  present 
next  to  the  diabase,  as  previously  mentioned. 

The  blue  conglomerate  appears  to  lie  at  the  bottom  of  a series  of 
carbonaceous  shales  which  are  partially  exposed  along  the  Mount 
Hope  road,  and  are  well  exhibited  2 miles  farther  west  in  a cutting 
along  the  Cornwall  and  Lebanon  Railroad.  On  the  geologic  maps 
(Pis.  II  and  IV)  the  conglomerate  and  carbonaceous  shales  are 
represented  by  one  pattern. 

The  area  over  wThich  the  ore-bearing  strata  were  naturally  ex- 
posed or  have  been  revealed  by  stripping  is  roughly  4,000  feet  long 
and  from  400  to  800  feet  wide,  and  its  extent  beneath  a superficial 
covering  of  loose  gravel  and  sandstone  debris,  though  as  yet  not 
fully  determined,  would  seem  to  be  considerably  more.  From  dia- 
mond-drill borings  south  of  the  present  workings  it  is  known  that 
ore  continues  in  this  direction  for  at  least  several  hundred  feet 
beyond  the  edge  of  the  Newark  strata  that  cap  the  deposit,  but  the 
information  afforded  by  these  holes  has  not  been  available  in  the 
present  study. 


OLOGICAL  SURVEY 


.ETIN 


GEOLOGIC  SKETCH  MAP  OF  VICINITY  OF  CORNWALL,  LEBANON  COUNTY,  PA. 


CORNWALL  DEPOSITS. 


19 


DIABASE  INTRUSIONS. 

The  diabase  next  to  the  Cornwall  deposit  is  an  intrusive  mass  of 
considerable  size  and  of  complex  shape.  Along  the  north  slope  of  the 
hills  that  face  the  Lebanon  Valley  its  outcrop  forms  a continuous 
east-west  band  from  a third  to  a half  mile  in  width  and  9 miles 
in  length.  This  body  is  connected  by  two  southward-trending  arms 
with  a second  band,  which  lies  about  2 miles  farther  south  and 
extends  with  a west-southwest  course  across  the  Susquehanna  into 
York  County.  This  southern  mass  of  diabase  has  the  form  of  a sill 
which  follows  a group  of  carbonaceous  shales  showing  generally 
northward  dips.  Shales  of  the  same  group  may  be  traced  along  the 
edges  of  the  connecting  arms  both  east  and  west  of  the  Cornwall 
mines,  and  though  local  crosscutting  may  be  noted,  it  is  evident  from 
the  field  relations  that  these  surface  connections  are  merely  portions 
of  the  extensive  sill  that  have  been  uncovered  by  erosion.  On  the 
other  hand,  the  diabase  of  the  northern  band  is  a crosscutting 
mass,  for  it  is  bounded  on  the  extreme  west  by  massive  sandstones 
of  the  Mesozoic;  then  by  the  same  rocks  on  tlie  south  and  by 
Paleozoic  limestones  on  the  north;  next,  just  south  of  Bismarck,  by 
black  Mesozoic  shales  on  both  sides ; farther  east  by  these  shales  and 
blue  conglomerate  on  the  south  and  by  the  slates  which  form  Mill 
Ridge  on  the  north;  at  the  mines  by  the  limestones  impregnated  with 
ore  and  the  slates  of  Mill  Ridge ; east  of  the  mines  as  far  as  Rexmont 
by  these  slates  on  both  sides;  and  thence,  to  a point  beyond  the 
Lebanon  waterworks  main  reservoir,  b}^  Paleozoic  limestones  on  the 
north  and  by  Mesozoic  strata  on  the  south,  except  where  small  out- 
crops of  slate  and  limestone  just  south  of  the  dike  have  been  re- 
vealed by  two  of  the  three  streams  that  supply  the  waterworks. 
(Through  an  error  only  two  of  these  streams  appear  on  the  sketch 
map,  PI.  II.) 

From  the  conclusions  that  the  southern  diabase  band  is  the  crop- 
ping of  a sill  and  that  the  northern  band  is  a dike,  it  is  but  a natural 
step  to  regard  the  latter  as  having  been  the  feeder  of  the  former ; and 
the  warrantable  belief  that  this  is  the  actual  relation  forms  the  basis 
of  the  structure  represented  in  the  cross  sections  (PL  III).  That 
there  is  a connection  between  the  dike  and  sill  in  the  vicinity  of  the 
mines  is  indicated  by  the  reported  presence  of  diabase  beneath  the 
ore-bearing  strata  in  all  the  diamond-drill  holes  that  have  been  bored 
south  and  southwest  of  the  present  workings.  It  is  hardly  to  be 
doubted  that  the  sill  forms  a continuous  sheet  beneath  the  oblong 
'area  about  6 square  miles  in  extent,’  which  is  surrounded  by  an  un- 
broken outcrop  of  the  diabase. 


20  MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 

STRUCTURE  OF  THE  BEDS. 

Within  this  area,  rimmed  by  diabase,  the  observed  dips  are  toward 
the  north,  and  the  average  inclination  of  the  strata  has  been  taken 
by  Lesley  and  D’Invilliers  ° to  be  between  12°  and  15°.  If,  however, 
the  diabase  mass  be  accepted  as  a sill  following  the  group  of  car- 
bonaceous beds,  it  is  evident  from  the  distribution  of  these  shales  that 
in  that  part  of  the  area  lying  west  of  the  Cornwall  Railroad  the 
effective  dip  toward  the  north  must  be  much  less  than  12°,  because 
the  shales  outcrop  on  the  south  side  at  elevations  between  700  and 
800  feet,  and  just  south  of  the  mines  their  croppings  are  barely  100 
feet  lower.  East  of  the  railroad  the  strata  may  be  somewhat  more 
steeply  inclined,  as  higher  and  higher  horizons  of  the  Mesozoic  strata 
come  into  contact  either  with  the  diabase  dike  or,  with  the  slates 
which  adjoin  it  for  nearly  2 miles  eastward  from  Miners  village. 
In  this  direction  it  seems  that  the  carbonaceous  shales  are  overlapped 
by  higher  beds  of  sandstone  and  red  shales,  so  that  their  contact  with 
the  Paleozoic  rocks  may  lie  well  back  from  the  edge  of  the  diabase 
dike  and  some  distance  below  the  lowest  Mesozoic  strata  locally 
exposed  by  the  stream  cuttings. 

In  Lancaster  County  (Pis.  II  and  III),  beyond  the  southern  edge 
of  the  sill,  lower  and  lower  Mesozoic  strata  emerge,  with  east-north- 
east  strikes  and  constantly  increasing  northward  dips,  until  the 
boundary  with  underlying  slates  is  encountered  about  2 miles  south 
of  Penryn.  The  basal  contact  on  this  side  of  the  Mesozoic  belt  is  a 
nearly  straight  line,  trending  slightly  south  of  west,  extending  from 
Hopeland  past  Brickerville  to  the  bend  of  Chickies  Creek,  just  north 
of  Whiteoak  station,  and  thence  nearly  to  Mastersonville,  where  it 
takes  a more  southerly  course,  reaching  Susquehanna  River  at  Bain- 
bridge.  Near  this  southern  boundary  the  dips  of  the  Mesozoic  strata 
are  steep  and  locally  are  even  overturned.  Allowing  for  the  ob- 
served gradually  decreasing  inclination  toward  the  north,  we  have 
an  estimated  thickness  of  strata  amounting  to  about  6,500  feet  be- 
tween the  bottom  of  the  Mesozoic  and  the  group  of  carbonaceous 
shales  in  which  the  intrusive  sill  occurs ; yet  near  the  Cornwall  mines, 
barely  H miles  north  of  the  point  where  the  shales  outcrop,  and  south 
of  Bismarck,  about  2 miles' distant,  the  same  beds  are  seen  to  have 
been  deposited  directly  upon  the  Paleozoic  rocks.  This  striking  rela- 
tion and  its  proper  interpretation  have  an  evident  bearing  on  the 
correct  understanding  of  the  structural  features  of  the  Cornwall 
deposit,  and  consequently  on  any  attempt  to  determine  the  possibility 
of  the  existence  of  other  similar ’deposits  in  the  neighborhood.  The 
explanation  suggested  is  that  the  Mesozoic  beds  were  laid  down 
under  such  circumstances  that  successively  higher  strata  were  spread 


a Cornwall  iron-ore  mines  : Ann.  Rept.  Geol.  Survey  Pennsylvania  for  18S5,  1886. 


I 


D 


ALL,  LEBAIS 


GEOLOGICAL  survey 


BULLETIN  NO.  359  PL.  Ill 


SECTION  ALONG  LINE  E-F,  PL.  H 


Feet 

1000 

500 

0 Sea  level 


Feet 

1000 

500 

0 Sea  level 


Feet 

1000 


500 

0 Sea  level 


Horizontal  scale 
2 3 


5 miles 


STRUCTURE  SECTIONS  IN  VICINITY  OF  CORNWALL,  LEBANON  COUNTY,  PA. 


CORNWM.L 

STATfPN/ 


tuZl'£i™ 


tOFF!CC  ' 

c3-f> 

,\SUPT  'c 


GEOLOGIC  MAP  OF  CORNWALL  MINES  AND  VICINITY,  LEBANON  COUNTY,  PENNSYLVANIA 


LEGEND 


Mesozoic 
conglomerates, 
sandstones  and  shales 


Blue  conglomerate 
Led  at  "base  of 
Mesozoic 


Paleozoic 
No. II  limestone 
and  limy  shale , 
the  latter  partly 
converted  into  ore 


Paleozoic  No.HI  slate 
' Mill  Hill'' slate  of 
Le  sley  and 
D'lnvOliers 


Intrusive 

diahase 


Contour  interval  & feet 
Datum  is  mean  sea  level 
1908 


1500 


CORNWALL  DEPOSITS. 


21 


farther  and  farther  toward  the  north  against  a continually  receding 
shore.  In  other  words,  the  facts  observed  indicate  that  the  Mesozoic 
basin  was  sinking  and  widening  as  deposition  went  on,  so  that  from 
south  to  north  there  is  a marked  overlap  of  the  Mesozoic  strata  upon 
the  Paleozoic  basement.  On  the  assumption  that  to  this  overlap  is 
due  the  disappearance  of  the  lower  strata  toward  the  north,  a struc- 
ture section  from  Lebanon  to  Whiteoak  station  has  been  drawn  to 
show  the  general  relations  of  the  rocks  (PI.  III).  The  north  end  of 
the  section  as  far  as  Mill  Kidge  has  been  copied  from  the  report  of 
Lesley  and  DTnvilliers.®  It  is  to  be  observed  that  inasmuch  as  noth- 
ing is  known  concerning  the  width  of  the  dike  below  ground  or  the 
attitude  of  its  walls  in  depth  the  representation  of  these  features  on 
the  section  is  entirely  conjectural;  also  that  in  showing  the  Paleozoic 
limestone  and  slate  beneath  the  Mesozoic  rocks  the  intention  is 
merely  to  suggest  that  they  form  a basement  upon  which  the  younger 
strata  were  deposited,  and  not  to  present  even  a guess  concerning  the 
structure  or  distribution  of  these  formations  underground. 

EXTENT  OF  THE  DEPOSITS. 

General  statement. — Attention  may  now  be  directed  to  the  manner 
in  which  the  Cornwall  deposits  embody  all  the  favorable  conditions 
listed  on  page  16.  They  occur  next  to  a considerable  body  of  diabase, 
which  exhibits  crosscutting  relations  to  the  stratified  rocks  adjacent. 
They  are  confined  to  limestone  strata  cut  by  this  diabase,  and  these 
beds  of  the  limestone  are  capped  both  by  Paleozoic  slates  and  by 
Mesozoic  carbonaceous  shales.  Metamorphism  of  the  sort  which  has 
affected  the  limy  strata  is  almost  lacking  in  both  of  these  cap  rocks; 
and  though  they  are  baked  in  the  near  vicinity  of  the  diabase,  the  con- 
clusion seems  to  be  justified  that  they  wTere  not  permeated  by  the 
mineralizing  waters  to  the  same  extent  that  the  limestones  were.  It 
seems  a fair  assumption  that  these  rocks  w7ere  from  their  nature  rela- 
tively impervious  to  the  solutions  which  formed  the  ore,  and  that  they 
served  in  a very  important  degree  to  prevent  the  dispersion  of  these 
waters  and  to  confine  their  movements  and  effects  to  the  limestones 
and  limy  shales  beneath  them,  a great  body  of  which  had  been  caught 
up  in  the  angle  between  the  crosscutting  dike  on  the  north  and  the  sill 
extending  out  toward  the  south.  There  is  every  reason  to  believe  that 
the  great  magnetite  deposit  at  the  Cornwall  mines  was  formerly 
capped  entirely  over  by  beds  of  sandstone  and  shale,  and  that  the  ap- 
pearance of  the  ore  body  at  the  surface  is  due  to  rather  modern  ero- 
sion. If  so,  two  questions  which  naturally  present  themselves  are: 
(1)  What  part  of  this  deposit  is  still  buried  beneath  barren  rock? 

a Cornwall  iron-ore  mines  : Ann.  Rept.  Geol.  Survey  Pennsylvania  for  1885,  1886,  p.  526. 


22 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


(2)  Is  it  not  probable  that  at  other  localities  in  the  vicinity  there  are 
like  deposits  which,  though  not  uncovered  by  natural  processes,  may 
be  found  by  exjiloration  ? 

The  Cornwall  ore  body—  Diamond  drilling  noAv  (1906)  in  progress 
will,  if  systematically  continued,  eventually  delimit  the  Cornwall  ore 
body.  From  a geologic  point  of  view  the  strata  which  carry  the  ore 
may  be  expected  to  run  out  under  the  Mesozoic  cover  toward  the  south 
in  the  form  of  a wedge,  the  thin  edge  of' which  will  be  encountered 
where  the  sill  of  diabase,  rising  toward  the  south,  reaches  the  uncon- 
f ormable  surface  between  the  ore-bearing  strata  and  the  overlying 
carbonaceous  shales  (PL  III).  That  magnetite  should  continue  to 
form  so  large  a proportion  of  the  rock  in  this  direction  as  it  does  near 
the  crosscutting  dike  seems  improbable  from  the  theory  which  has 
been  stated  concerning  the  origin  of  the  ores. 

Just  west  of  the  Grassy  Hill  mine  the  diabase  is  seen  on  the  sur- 
face to  trend  directly  across  the  strike  of  the  ore-bearing  strata  and 
to  come  into  contact  with  the  overlying  slate,  which  is  exposed  on 
the  north  slope  of  the  little  knoll  west  of  the  Mount  Hope  wagon 
road.  It  seems  possible  that  the  limy  beds  which  elsewhere  carry 
the  ores  may  be  present  beneath  this  patch  of  slate,  but  farther  west, 
where  the  carbonaceous  shales  appear  in  contact  with  the  diabase, 
the  sill  seems  to  be  entering  this  group  of  beds,  so  that  in  this  vicinity 
there  is  no  place  south  of  the  dike  for  the  limestone  beds  to  be  present 
except  beneath  the  sill.  Starting  from  a point  about  1,000  feet  Avest 
of  the  Mount  Hope  \ATagon  road,  AAThere  the  carbonaceous  shale  over- 
laps the  slate  and  comes  into  contact  with  the  diabase,  an  irregular 
line  drawn  to  the  southern  edge  of  the  ore-bearing  strata,  when  the 
position  of  this  edge  is  determined  by  the  drill,  will  indicate  the 
general  limit  of  these  strata  south  and  southwest  of  Grassy  Hill. 

East  of  the  railroad  and  south  of  the  diabase  hook  which  forms 
the  south  side  of  Big  Hill,  the  ore-bearing  strata  should  be  present 
just  beneath  the  rather  thick  cover  of  surface  debris.  Slates  appear 
on  the  hill  slopes  north  of  the  eastern  part  of  Miners  ATillage,  and 
as  these  beds  are- known  to  lie  stratigrapliically  aboA^e  the  limy  beds, 
the  latter  are  probably  in  contact-  Avith  the  diabase  dike  at  a moderate 
depth  beneath  the  capping  of  slate. 

The  slates  continue  as  a narroAv  band  from  Miners  Aullage  to  the 
Rexmont-0\Terlook  road.  The  presence  or  absence  of  the  uppermost 
strata  of  the  ATalley  liniestone  immediately  beneath  the  slate,  and, 
if  present,  the  thickness  of  the  mass,  are  dependent  on  the  local  ex- 
istence of  a direct  connection  betAveen  the  dike  and  the  sill  and  on 
the  depth  at  which  they  join.  It  is  evident  that  if  a connection 
between  the  sill  and  the  dike  exists  just  beneath  the  slate  there  can 
be  no  limestone  aboAre  the  sill,  and  that  the  deeper  the  connection  the 


CORNWALL  DEPOSITS. 


23 


thicker  will  be  the  mass  of  limestone  caught  in  between  the  dike 
and  the  sill.  However  far  the  limestone  strata  may  extend  along 
the  southern  wall  of  the  dike,  which  trends  northeastward  from 
Miners  village,  just  so  far  are  the  structural  relationships  between 
the  different  sorts  of  rock  similar  to  those  which  have  favored  the 
deposition  of  ore  at  the  Cornwall  mines.  All  of  this  ground,  as  far 
as  the  road  leading  from  Rexmont  to  Overlook,  is  regarded  as  likely 
to  contain  a continuation  of  the  Cornwall  ore  bed  and  to  warrant 
such  expenditure  as  would  be  required  to  prospect  it  adequately. 
(See  Rexmont-Overlook  section,  Pl.  III.) 

To  summarize,  it  seems  that  exploration  should  be  extended  along 
the  strike  of  the  deposit  for  about  1,000  feet  toward  the  west  and  for 
at  least  5,000  feet  toward  the  east. 

Near -by  deposits. — In  regard  to  the  possibility  that  similar  depos- 
its may  occur  in  other  localities,  it  may  be  said  that  from  the  geologic 
point  of  view  they  may  very  well  exist  in  several  places. 

East  of  the  Rexmont-Overlook  wagon  road  the  southern  edge  of 
the  Cornwall  diabase  dike  exhibits  a crosscutting  contact  with  the 
Mesozoic  beds  as  far  as  the  first  of  the  three  creeks  which  afford  Leb- 
anon’s water  supply.  Here  outcrops  of  slate  on  the  western  bank  of 
the  stream  and  next  to  the  diabase  presumably  correspond  with  the 
slate  occurring  in  Mill  Ridge  and  on  the  opposite  or  south  side  of 
the  dike  in  the  neighborhood  of  the  Cornwall  mines.  On  the  ridge 
above  this  outcrop  Mesozoic  rocks  are  found,  and  the  surface  of  over- 
lap or  unconformity  lies  somewhere  between. 

The  next  ravine  to  the  east  has  been  dammed  to  form  a collecting 
reservoir,  along  the  shores  of  which  flat-lying  strata  of  shale  and 
limestone  are  well  exposed.  During  the  construction  a mass  of  mag- 
netite, which,  though  it  proved  to  be  a pocket,  is  said  to  have  fur- 
nished 500  tons  of  ore,  was  encountered  in  an  excavation  on  the  east 
side  of  the  creek  below  the  dam.  F rom  what  may  be  seen  at  present, 
it  is  evident  that  this  pocket  of  ore  occurred  between  the  wall  of  the 
diabase  dike  and  limy  strata  lying  just  under  the  overlapping  Meso- 
zoic beds.  All  the  sedimentary  rocks  are  considerably  metamor- 
phosed, silicate  minerals  and  small  segregation  of  specular  hematite 
being  largely  developed  in  the  Mesozoic  strata  for  several  hundred 
feet  to  the  south. 

Several  years  ago  the  Lackawanna  Iron  and  Steel  Company  put 
down  three  test  holes  in  this  vicinity,  hoping  to  develop  a workable 
deposit  of  magnetite.  Hole  No.  1 was  situated  a short  distance  north 
of  the  excavation  referred  to  above,  No.  la  about  125  feet  farther 
north,  and  No.  2 on  the  ridge  about  300  feet  east  of  the  excavation 
and  about  120  feet  above  the  creek.  The  following  records  of  these 
holes  have  been  furnished  by  the  company : 


24 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Earth.  _ 
Diabase. 


Earth__. 

Diabase 


Records  of  drill  holes  near  collecting  reservoir. 


hole  No.  1. 

Feet. 

4i 

141i 


146 

HOLE  No.  la. 

10£ 

91  i 


HOLE  No.  2. 


Earth 

Soft  sandstone- . 

Diabase 

White  limestone. 
Diabase 


102 


Feet. 
41 
26i 
54  2 
24 
27 


173 


The  configuration  of  the  surface  is  such  that  hole  No.  2,  though 
173  feet  deep,  penetrated  only  51  feet  below  the  level  of  the  stream. 
Two  interpretations  may  be  placed  on  the  section  determined  by  hole 
No.  2 — that  the  two  bodies  of  diabase  are  wedges  from  the  main  dike 
extending  out  into  the  stratified  rocks,  or  that  there  is  here  merely  a 
waving  contact  between  the  dike  and  the  stratified  rocks  penetrated 
by  it.  A hole  situated  100  feet  or  more  farther  south  might  be  ex- 
pected to  encounter  a greater  thickness  of  Paleozoic  limestone,  and 
there  is  the  possibility  that  certain  layers  might  be  impregnated  with 
magnetite.  On  the  whole,  in  spite  of  the  unfavorable  result  of  the 
tests  mentioned  above,  it  seems  that  it  may  yet  be  worth  while  to 
make  further  explorations  along  the  south  side  of  the  Cornwall  dike 
from  the  reservoir  westward  to  the  Rexmont-Overlook  road,  and, 
as  already  suggested,  thence  to  Miners  village.  In  all  probability  a 
bore  hole  situated  100  or  200  feet  south  of  hole  No.  2 on  the  ridge 
above  the  reservoir  would  penetrate  a considerable  thickness  of 
Paleozoic  limestone  beneath  the  overlapping  Mesozoic  beds,  and  there 
is  no  obvious  reason  why  certain  layers  of  the  limestone  may  not  be 
replaced  by  magnetite. 

Eastward  from  the  reservoir,  where  the  pocket  of  ore  was  found, 
the  limestone  lying  beneath  the  Mesozoic  beds  can  not  extend  far 
before  being  cut  by  the  dike,  which  within  a short  distance  turns 
southward  into  the  Mesozoic  area  and  changes  from  a strongly  cross- 
cutting dike  to  a sill  following  the  bedding  of  the  Mesozoic  rocks. 

In  all  probability  a bore  hole  or  shaft  less  than  50  feet  deep  lo- 
cated above  the  diabase  in  the  ravine  southeast  of  Rexmont  would 
reveal  slate  or  limestone,  either  one  of  which  if  present  would  war- 
rant deeper  exploration,  even  if  no  ore  were  discovered  in  the  upper- 
most layers  of  the  limestone.  A fact  which  would  seem  to  mark  this 
as  a promising  place  for  prospecting  is  the  occurrence  of  ore  on  the 
opposite  side  of  the  diabase  dike  at  the  old  Doner  mine  northeast  of 
Rexmont. 

The  southern  border  of  the  Cornwall  diabase  dike  westward  from 
its  junction  with  the  sill  southwest  of  Cold  Spring  crossing  shows  a 


CORNWALL  DEPOSITS. 


25 


strongly  crosscutting  contact  with  massive  Mesozoic  sandstones.  Be- 
tween this  contact  and  the  outcrop  of  the  diabase  sill  to  the  south  no 
detailed  observations  have  been  made,  so  that  little  definite  informa- 
tion concerning  the  structure  of  the  area  of  Mesozoic  rocks  lying 
north  and  south  from  the  Cornwall  and  Lebanon  Railroad  is  at  hand. 
However,  red  sandstone  beds  exposed  near  the  railroad  crossing  one- 
half  mile  northeast  of  Mount  Gretna  station  show  a dip  of  about 
25°  X.,  and  the  contour  of  the  west  edge  of  the  sill  between  the  moun- 
tain known  as  Governor  Dick  and  the  railroad  west  of  Cold  Spring 
crossing  likewise  indicates  a strong  inclination  of  the  strata  in  a 
northerly  direction.  Furthermore,  only  northerly  dips  are  observed 
south  of  the  railroad  along  the  outcrop  of  the  sill,  and  it  is  fairly 
assumable  that  the  whole  block  between  the  two  bands  of  diabase  is 
rather  strongly  tilted  in  this  direction.  If  this  is  accepted  as  a fact, 
the  group  of  carbonaceous  shales  would  nowhere  meet  the  cross- 
cutting dike  less  than  100  feet  belowT  the  contact  line  as  seen  on  the 
surface,  except  within  a few  hundred  feet  from  the  point  where  the 
southern  edge  of  the  dike  crosses  the  wagon  road  west  of  Cold 
Spring.  As  the  sill  is  known  to  lie  in  the  carbonaceous  shales  for  a 
long  distance  westward  from  the  headwaters  of  Chickies  Creek,  and 
also,  as  it  follows  these  strata  both  east  and  west  to  Cold  Spring  cross- 
ing, it  seems  most  likely  that  it  continues  to  occupy  this  position  be- 
neath the  Mount  Gretna  block  all  the  way  from  the  southern  outcrop 
to  its  buried  junction  with  the  feeding  dike.  This  probability 
points  to  the  failure  of  explorations  which  might  be  undertaken  be- 
tween the  Cornwall-Colebrook  road  and  the  diabase  dike,  with  the 
expectation  of  locating  limestone  strata  in  contact  with  the  diabase 
dike,  unless  the  search  be  extended  beneath  the  sill  of  diabase. 

Along  its  northern  edge  the  diabase  dike  is  bounded  in  different 
parts  of  its  course  by  four  distinct  sets  of  strata.  On  the  extreme 
west  its  northern  wall  is  formed  by  Mesozoic  sandstones  for  a dis- 
tance of  1J  miles  to  a point  a short  distance  wrest  of  the  wagon  road 
leading  from  the  Horseshoe  pike  to  Mount  Gretna  (PI.  II) . From  this 
place  to  the  next  north-south  road  the  bounding  rock  is  evidently 
limestone,  though  the  line  of  contact  is  completely  obscured  by  a cover 
of  surface  debris.  The  boundary  has  been  represented  on  the  map  by 
a random  line,  the  accuracy  of  which  might  possibly  be  improved 
by  more  detailed  examination  than  has  as  yet  been  made  in  this 
vicinity.  On  general  principles  this  contact  may  be  included  among 
favorable  situations  for  the  occurrence  of  iron  ore,  though  but  little 
emphasis  is  placed  on  the  suggestion  in  view  of  the  very  slight  studv 
which  has  been  given  to  the  localit}^.  Should  the  surface  wash  prove 
to  be  as  deep  as  it  seems  to  be  at  first  glance,  failure  to  have  dis- 
covered float  ore  in  tilling  the  fields  can  not  be  regarded  as  a strong 
argument  against  the  possibility  of  ore  masses  being  present  in  the 


26 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


limestone  near  the  wall  of  the  intrusive  dike.  The  only  one  of  the 
five  features  favorable  to  ore  segregation  mentioned  on  page  16  which 
seems  lacking  in  this  vicinity  is  an  impermeable  cap  rock  over  the 
strata  lying  adjacent  to  the  diabase.  At  the  same  time  the  lime- 
stones do  not  include  the  strata  immediately  beneath  the  slates  which 
comprise  the  ore-bearing  beds  at  Cornwall. 

Farther  east  there  is  an  extensive  patch  of  carbonaceous  shale  be- 
tween the  valley  limestone  and  the  diabase.  Being  identical  in  ap- 
pearance with  the  Mesozoic  black  shales  in  the  railroad  cutting  on 
the  south  side  of  the  dike,  within  the  narrow  angle  between  the  dike 
and  the  sill,  these  beds  are  supposed  to  belong  to  the  same  horizc. . 
They  lie  nearly  horizontal,  and  are  supposed  to  rest  directly  upon  the 
limestone  or  possibly  in  part  upon  slate,  as  do  similar  beds  just  south 
of  the  ore  banks.  Every  geologic  consideration  points  to  this  as  good 
prospecting  ground.  It  may  be  that  slates  (corresponding  to  those 
which  outcrop  in  the  wagon  road  one-half  mile  southwest  of  Bis- 
marck) lie  between  the  carbonaceous  shale  and  the  limestones  in  the 
vicinity  of  the  diabase  contact,  but  somewhere  at  no  great  depth  beds 
of  limestone  belonging  to  the  same  horizons  as  those  which  have  been 
converted  into  ore  at  the  Cornwall  mines  must  come  into  contact  with 
the  intrusive  diabase.  Capped  as  these  beds  are  by  strata  only 
slightly  permeable  by  circulating  waters,  the  conditions  would  seem 
to  be  very  similar  to  those  which  led  to  the  production  of  the  Corn- 
wall deposit.  If  the  boundary  between  the  shales  and  the  diabase 
can  be  taken  to  indicate  the  general  shape  of  the  northern  wall  of  the 
dike,  there  is  here  an  embayment  from  the  north  resembling  in  a 
way  the  one  from  the  south,  which  is  occupied  by  the  Cornwall 
deposit. 

From  the  Bismarck-Mount  Hope  road  to  Rexmont  the  Cornwall 
diabase  dike  is  bounded  on  the  north  by  slates,  which  occupy  a band 
BOO  to  400  feet  wide  along  a line  of  hills  known  as  Mill  Ridge.  These 
slates  were  assigned  by  Lesley  and  DTnvilliers  to  44  Formation  No. 
Ill  ” of  the  Pennsylvania  Paleozoic  section,  and  they  were  regarded  as 
resting  conformably  upon  the  limestones  of  44  No.  II,”  with  a generally 
rather  low  dip  toward  the  south.  These  suggestions  seem  entirely 
correct,  and  it  is  concluded  that  as  far  as  these  slates  extend  east  and 
west  along  the  . north  side  of  the  diabase  dike  the  uppermost  beds  of 
the  valley  limestone,  or  44  Formation  No.  II,”  must  come  into  contact 
with  the  diabase  at  a very  -moderate  depth  and  offer  a favorable  con- 
dition for  the  existence  of  iron  ore.  Though  this  suggestion  is  made 
entirely  on  the  basis  of  the  principles  set  down  on  page  16,  it  finds 
strong  corroboration  in  the  fact  that  ore  occurs  just  beyond  the 
eastern  outcrops  of  the  slate  at  the  old  Doner  mine.  The  strata  in 
which  the  ore  occurs  at  this  point  are  evidently  to  be  included  among 
the  uppermost  layers  of  the  valley  limestone,  and  their  contact  with 


CORNWALL  DEPOSITS. 


27 


diabase,  though  hidden  by  surface  wash,  can  not  be  far  distant  from 
the  mine.  It  is  believed  that  the  geologic  features  of  the  Doner  mine 
are  essentially  those  which  exist  beneath  the  surface  for  more  than 
2 miles  westward  from  Rexmont,  and  there  is  every  indication  that 
the  rocks  are  identical  in  stratigraphic  position  with  those  which 
contain  the  great  deposit  of  ore  in  the  Cornwall  mines.  Separated 
from  the  mines  only  by  the  dike  of  diabase  held  to  be  responsible 
for  the  segregation  of  iron  in  the  deposits  already  known  and  worked, 
this  ground  would  seem  worthy  of  systematic  exploration. 

From  the  north-south  road  leading  to  Rexmont  as  far  eastward  as 
Horst’s  mill,  deep  wash  derived  from  the  near-by  hills  completely 
hides  the  northern  edge  of  the  diabase  dike,  and  it  is  only  at  the 
Doner  mine  that  rocks  near  the  contact  are  exposed  at  all,  and  even 
here  nothing  definite  can  be  made  out  regarding  the  attitude  of  the 
strata.  The  mine  is  said  to  have  furnished  5,000  tons  of  ore  similar 
in  every  way  to  the  surface  ore  at  the  Cornwall  banks  but  occurring 
intermixed  with  loose  sand.  The  pit  from  which  the  ore  was  mined 
is  now  completely  caved  in,  but  seems  to  have  been  40  or  50  feet  wide 
and  perhaps  250  feet  long.  North  of  the  workings  bowlders  of  hard 
magnetite  are  found  in  the  soil  over  an  area  700  to  800  feet  square. 
This  material  is  supposed  to  be  float  from  the  Doner  deposit.  Sev- 
eral years  ago  two  or  three  holes  were  drilled  on  this  property,  but 
beyond  the  report  that  no  attractive  ore  body  was  encountered  records 
of  this  work  have  not  been  procured.  From  the  fact  that  the  old 
workings  extended  east  and  west,  three  possibilities  may  be  consid- 
ered as  to  the  shape  of  the  ore  mass  in  its  original  state,  before  it 
became  broken  down  by  surficial  weathering,  and  it  is  believed  that 
negative  results  at  this  place  are  not  to  be  considered  as  finally  ad- 
verse to  the  presence  of  a workable  ore  body  until  tests  have  been 
carried  out  with  reference  to  each  of  these  possibilities:  (1)  The 
impregnated  rock  may  have  been  a layer  in  the  limestone  capped  over 
by  a barren  stratum.  If,  then,  the  beds  have  a southward  dip  the 
edge  of  the  diabase  may  lie  some  distance  to  the  south;  (2)  the  ore 
may  have  formed  along  the  wall  of  the  dike  as  a replacement  of  a 
limited  amount  of  limestone  in  contact  with  the  intrusive  rock;  in 
this  case  the  diabase  would  be  found  very  near  the  old  workings; 
(3)  the  ore  may  have  been  deposited  along  the  walls  of  a fissure 
running  parallel  with  the  wall  of  the  dike,  but  at  some  distance  from 
it.  The  deposit  of  ore  at  the  old  Carper  mine,  8 miles  west  of  Corn- 
wall, seems  to  have  had  this  origin. 

The  contact  of  diabase  with  the  valley  limestone  eastward  from 
the  Doner  property  to  the  main  reservoir  of  the  Lebanon  waterworks 
is  hidden  by  a heavy  apron  of  sandstone  debris,  so  that  the  line 
representing  the  boundary  on  the  sketch  map  is  only  an  approxima- 
tion. Though  ore  may  occur  along  this  contact,  prospecting  would 


28 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


hardly  be  taken  up  unless  favorable  results  had  been  obtained  in  some 
of  the  more  accessible  localities  suggested  above. 

MINES  WEST  OF  CORNWALL. 

Near  the  edge  of  the  Mesozoic  belt  between  Cornwall  and  Susque- 
hanna River  there  are  two  minor  occurrences  of  magnetic  ore — one 
at  the  old  Carper  mine  in  Lebanon  County,  about  1 mile  southeast  of 
Mount  Pleasant,  the  other  in  Dauphin  County,  about  2 miles  south- 
east of  Hummelstown. 

CARPER  DEPOSIT. 

The  Carper  deposit,  from  which  1,500  tons  of  ore  have  been  mined, 
appears  to  lie  in  a fault  break,  which  may  be  regarded  as  a westward 
extension  of  the  fissure  which  holds  the  Cornwall  diabase  dike.  North 
of  the  ore  pit  the  rocks  are  Paleozoic  limestone,  while  to  the  south 
are  baked  shales,  followed  by  diabase.  The  shales  were  regarded  by 
Lesley  and  D’Invilliers  as  equivalent  to  the  slates  of  Mill  Ridge 
occurring  at  Cornwall,0  but  to  the  writer  they  seem  to  belong  with  the 
Mesozoic  strata. 

The  diabase  which  outcrops  south  of  the  mine  is  a sill  which  fol- 
lows the  Mesozoic  strata.  The  sill  strikes  northeast  and  southwest, 
and  dips  toward  the  northwest.  The  trend  of  the  diabase  is  diagonal 
to  the  course  of  the  fault,  and  the  intrusive  rock  does  riot  continue 
north  of  the  break.  On  the  geologic  map  (PL  II)  it  has  been  repre- 
sented as  ending  at  the  fault,  though  exposures  are  not  sufficient  to 
show  that  it  actually  extends  as  far  toward  the  northeast.  Toward 
the  southwest  the  diabase  widens  in  outcrop  and  is  known  to  consti- 
tute a large  mass.  The  sandstones  and  shales  near  it  are  strongly 
baked  or  indurated,  and  are  also  bleached  to  a considerable  extent. 
The  occurrence  of  the  ore  in  the  fault  fissure,  the  presence  of  the  igne- 
ous rock  near  by,  and  the  fact  that  the  inclination  of  the  diabase  mass 
toward  the  north  and  northwest  wTould  carry  it  beneath  the  place 
where  the  ore  outcrops  make  it  probable  that  the  deposit  was  formed 
by  solutions  circulating  along  the  fault  break  and  impelled  by  the 
heat  of  the  buried  diabase.  If  the  true  relations  of  the  deposit  are 
as  here  suggested,  the  ore  should  persist  in  depth  and  should  also 
occur  at  other  points  along  the  fault  both  east  and  west  of  the  old 
mine.  Though  the  exact  position  of  the  fault  is  hidden  by  over- 
washed debris  from  the  adjacent  hills,  no  serious  difficulty  would  be 
experienced  in  finding  it  by  means  of  excavations.  This  fault  ap- 
pears to  be  the  westward  extension  of  the  fissure  occupied  by  the 
crosscutting  mass  of  diabase  at  Cornwall. 

Iron  ore  is  reported  to  occur  about  1 mile  southwest  of  Mount 
Pleasant,  where  some  prospecting  was  done  several  years  ago.  This 


a Ann.  Rept.  Geol.  Survey  Pennsylvania  for  1885,  1886,  p.  544. 


BERKS  COUNTY  DEPOSITS. 


29 


locality  was  not  found,  and  it  is  not  known  that  the  ore  is  of  the 
Cornwall  type.  In  this  neighborhood  the  Paleozoic  limestones  con- 
tain several  masses  of  intrusive  diabase,  so  that  it  would  not  be  at 
all  surprising  to  find  ore  like  that  of  the  Cornwall  mine. 

HUMMELSTOWN  DEPOSITS. 

The  deposits  2 miles  southeast  of  Hummelstown  are  situated  well 
within  the  belt  of  Mesozoic  rocks  on  the  east  side  of  Walton ville 
Brook.  The  ore,  consisting  of  magnetite  and  specular  hematite  some- 
what contaminated  by  pyrite,  occurs  in  pockets,  several  of  which  have 
been  worked  out,  but  from  what  may  be  seen  the  deposits  could  hardly 
have  been  of  any  great  importance.  A small  amount  of  garnet  occurs 
with  the  ore  minerals.  The  old  workings  are  in  the  valley  of  a small 
stream  and  extend  in  a general  east-we^t  direction  for  a distance  of 
about  2,500  feet.  Except  along  the  wagon  road  there  are  few  ex- 
posures of  rock  in  place  in  the  vicinity.  North  of  the  ravine  in 
which  the  ore  pits  are  situated  the  strata  stand  in  nearly  vertical 
position,  but  south  of  the  ravine  the  beds  of  sandstone  have  a north- 
erly dip  of  about  20°.  From  these  observations  it  is  evident  that  the 
deposits  occur  adjacent  to  and  probabty  in  part  along  a strong  fault 
break.  Everywhere  in  the  vicinity  of  the  fault  the  sandstones  are 
greatly  bleached  and  indurated,  as  similar  rocks  are  elsewhere  in  the 
neighborhood  of  diabase  masses,  and,  though  no  outcrops  of  the 
igneous  rock  appear  in  the  immediate  vicinity,  it  is  believed  that 
diabase  must  be  present  at  some  unknown  depth  beneath  the  surface 
and  that  waters  heated  by  this  rock,  or  perhaps  derived  from  it,  were 
responsible  for  the  general  metamorphism  and  for  the  segregation  of 
the  iron  ores. 

Though  the  deposits  are  of  interest  to  the  student  of  ore  genesis, 
it  does  not  seem  that  they  offer  sufficient  encouragement  for  more 
extensive  exploration. 

BERKS  COUNTY  DEPOSITS. 

WHEATFIELD  GROUP. 

GENERAL  DESCRIPTION. 

The  Wheatfield  group  of  mines,  with  which  the  Ruth  mine  is  here 
included,  is  situated  about  7 miles  southwest  of  Reading  and  a short 
distance  southeast  of  Fritztown  station,  on  the  Columbia  division 
of  the  Philadelphia  and  Reading  Railroad.  (See  PI.  VI.)  In  their 
geologic  features  the  deposits  of  iron  ore  at  this  place  show  certain 
striking  resemblances  to  the  Cornwall  deposits  20  miles  to  the  west. 
The  ores  occur  as  irregular  masses,  having  a general  layer-like  form, 


BO 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


interbedded  with  limestone  strata,  but  the  ore  bodies  are  numerous 
rather  than  large,  and  lack  of  persistency  is  a marked  characteristic. 
In  respect  to  stratigraphic  position,  the  strata  which  carry  the  de- 
posits do  not  correspond  with  those  of  the  Cornwall  mine,  for  they 
apparently  belong  at  the  base  of  the  Paleozoic  limestones  (“  No.  II  ” 
of  the  Second  Pennsylvania  Survey),  as  at  the  Raudenbusch  and 
Island  mines  near  Reading  and  at  Boyertown.  This  conclusion  re- 
garding the  equivalence  of  these  strata  is  not  based  on  a critical  study 
of  the  question  by  the  present  writer,  but  is  deduced  from  recorded 
descriptions  by  D’Invilliers  and  from  the  distribution  of  the  Paleozoic 
formations  as  exhibited  on  his  geologic  map  of  Berks  County.® 

Like  the  deposits  at  Cornwall,  Reading,  and  Boyertown^and  at  the 
Jones  mine,  the  Wheatfield  deposits  occur  very  near  the  overlap  of 
Mesozoic  beds  and  adjacent  to  a large  intrusion  of  diabase. 

DIABASE  INTRUSION. 

The  ore-bearing  strata  appear  at  the  surface  along  the  east  and 
north  sides  of  a roughly  rectangular  area  of  sedimentary  rocks,  form- 
ing a northward  embay ment  in  the  principal  diabase  mass  of  the 
district.  The  greater  part  of  this  area,  which  is  nearly  a mile  long 
and  three- fourths  of  a mile  wide,  is  covered  by  Mesozoic  rocks.  The 
older  strata,  in  which  the  ore  occurs,  are  restricted  to  a band  150  to 
250  yards  wide  next  to  the  curving  edge  of  the  diabase  intrusion. 
The  south  edge  of  this  band  is  formed  by  the  overlap  of  the  Mesozoic 
beds,  south  of  which  there  is  an  outlying,  irregularly  shaped  mass  of 
diabase  opposite  the  embavment  in  the  main  intrusion.  (See  Pis. 
V and  VI.) 

The  mass  of  diabase  that  curves  around  the  Wheatfield  group  of 
mines  constitutes  the  western  termination  of  an  intrusion  which 
extends  7 miles  eastward  to  Schuylkill  River  and  thence  somewhat 
more  than  10  miles  in  a southeasterly  direction  along  the  western 
side  of  the  broad  Schuylkill  Valley  (PI.  V).  The  outcrop  of  this 
diabase  is  from  one- third  mile  to  1 mile  wide.  Throughout  the 
greater  part  of  its  course  it  lies  wholly  within  the  Mesozoic  area, 
where  it  has  the  form  of  a sill,  closely  following  the  stratification  of 
the  incasing  rocks.  Near  the  Schuylkill,  however,  where  its  course 
changes  from  east  to  southeast,  arid  also  near  the  Wheatfield  mines, 
marked  crosscutting  may  be  observed,  and  Paleozoic  as  well  as  Meso- 
zoic rocks  come  into  contact  with  the  diabase.  It  is  in  these  Paleo- 
zoic strata  near  the  diabase  that  the  ore  deposits  occur  at  the  Fritz 
Island  and  Raudenbusch  mines  south  of  Reading,  and  at  the  Wheat- 
field  mines  7 miles  farther  east.  (See  cross  sections,  figs.  1,  2,  and  3.) 

n Geology  of  the  South  Mountain  belt  of  Berks  County  : Second  Geol.  Survey  Pennsyl- 
vania, Kept.  D3,  pt.  1,  atlas,  1883.  • 


Dene 


READII 


SURVEY 


Mesozoic  red  sandstones  Mesozoic  limestone 

and  shales  conglomerate 


Paleozoic  limestones 
carrying  ore  deposits 


Diabase 


X X 

Mines  and  prospects 


GEOLOGIC  SKETCH  MAP  OF  DISTRICT  SOUTH  OF  READING,  BERKS  COUNTY,  PA. 


BERKS  COUNTY  DEPOSITS. 


31 


CHARACTER  OF  THE  ORES. 

The  Wheatfield  mines  have  not  been  extensively  worked  for  more 
than  twenty  years,  though  small  amounts  of  surface  ore  have  been 
extracted  from  time  to  time,  the  last  mining  having  been  done  in 
1905  and  1906.  The  ore  to  a depth  of  30  or  40  feet  is  reported  to  be 
invariably  soft  or  earthy,  evidently  as  a result  of  the  ready  decompo- 
sition of  the  original  ore,  owing  to  the  presence  of  considerable 
pyrite.  These  soft  ores  have  been  desired  by  ironmasters  for  mix- 
tures, but  the  unweathered  or  hard  ores  seem  to  have  found  little 
favor,  as  they  are  at  once  of  rather  low  iron  content  and  so  high  in 
sulphur  as  to  require  roasting  before  they  can  be  used  in  a blast  fur- 
nace. Apparently  for  this  reason,  and  because  the  deposits  are  not 
large  or  even  persistent,  these  mines  have  not  been  more  systematic- 
ally developed; 

STRUCTURE  OF  THE  ROCKS. 


Most  of  the  old  workings  of  the  group  are  situated  near  the  east 
side  of  the  area  of  sedimentary  rocks  which  sets  back  from  the  south 


Fig.  1. — North-south  structure  section  400  feet  east  of  Ruth  mine,  Wheatfield  group 

(along  line  A-A',  PI.  VI).  1,  Mesozoic  beds;  2,  Paleozoic  slate;  3,  Paleozoic  limestone; 

4,  diabase  intrusion. 

into  the  diabase  dike  and  south  of  the  east-west  public  road  which 
follows  the  upper  valley  of  Cacoosing  Creek.  About  a dozen  open 
pits  have  been  operated  at  various  times,  and  in  addition  many 
slopes  and  several  vertical  shafts.  Across  the  creek,  on  the  north 
side  of  the  wagon  road,  there  is  an  opening,  formerly  known  as 
slope  No.  1,  and  in  1905  some  surface  ore  was  taken  out  by  means  of 
a slope  located  a short  distance  east  of  these  old  workings.  The 
Ruth  mine  is  situated  about  one-half  mile  west  of  slope  No.  1,  about 
200  yards  east  of  the  direct  road  from  Fritztown  to  Adamstown. 

In  the  more  southerly  Wheatfield  workings  the  strikes  of  the  strata 
run  nearly  north  and  south,  as  shown  both  by  the  direction  in  which 
the  pit  workings  extend  and  by  the  beds  of  limestone  exposed  in  the 
old  excavations;  but  farther  and  farther  north  the  strata  turn  more 
and  more  toward  the  northwest  and  finally  run  nearly  east  and  west 
at  slope  No.  1.  Dips  are  here  invariably  toward  the  concave  edge 
of  the  curving  band  of  ore-bearing  rocks  and  away  from  the  Avail 
of  the  surrounding  diabase.  At  the  Ruth  mine,  Avhere  the  strata  are 


32 


MAGNETITE. DEPOSITS  IN  PENNSYLVANIA. 


fairly  well  exposed  in  the  open  cut,  the  stratification  is  found  to  be 
nearly  horizontal,  though  the  ore  body  is  reported  to  dip  30°  S., 
indicating  that  it  is  not  conformable  to  the  bedding  of  the  inclosing 
rocks.  Both  here  and  at  slope  No.  1 the  foot  wall  of  the  ore  is  dia- 
base and  the  immediate  hanging  wall  is  limestone  or  limestone  brec- 
cia. In  both  places  also  the  limestone  capping  above  the  ore  is  over- 
lain  by  slate,  and  in  the  hills  south  of  the  Ruth  mine  debris  of  this 
slate  and  a few  shallow  excavations  show  it  to  have  a thickness  of 
about  80  feet.  At  slope  No.  1 its  thickness  can  not  be  determined  and 
the  area  which  it  covers  can  not  be  defined,  owing  to  lack  of  exposures. 

No  stratum  corresponding  to  the  slate  mentioned  above  has  been 
encountered  in  the  workings  situated  south  of  the  public  road,  but 
the  changing  strike  of  the  bedding  toward  the  north  along  the  ore 
band  toward  slope  No.  1,  together  with  the  fact  that  the  limestone 
layers  in  the  Ruth  mine,  in  slope  No.  1,  and  in  several  of  the  southern 
workings  are  similarly  composed  of  fragments,  would  make  it  ap- 
pear that  the  strata  occurring  in  the  southward-trending  leg  of  the 


B-B' , PI.  VI).  1,  Mesozoic  beds;  2,  Paleozoic  slate;  3,  Paleozoic  limestone;  4,  Paleozoic 
quartzite  ; 5,  diabase  intrusion. 

strip  in  which  the  ore  is  found  lie  stratigraphically  below  the  bed  of 
slate.  In  this  case,  as  the  beds  dip  toward  the  west,  it  is  possible 
that  the  slate  may  be  present  west  of  the  main  workings  beneath  the 
surface  capping  of  the  Mesozoic  sandstones. 

Two  beds  of  limestone,  one  solid  and  the  other  made  up  of  frag- 
ments, are  exposed,  with  low  southerly  dips,  in  the  creek  bed  be- 
tween the  two  main  tributaries  from  the  south  (PL  VI).  These 
strata  are  supposed  to  correspond  with  those  in  the  main  Wheatfield 
workings,  and  their  presence  in  this  place  suggests  that  the  slate  at 
slope  No.  1 can  not  be  connected  by  continuous  outcrop  with  the  slate 
at  the  mine.  The  dips  at  the  two  places  are  not  in  accord,  and  it  may 
very  wTell  be  that  there  is  a fault  between. 

In  the  bed  of  the  more  westerly  of  the  two  northward-flowing 
brooks  (PI.  VI),  500  or  GOO  feet  above  its  junction  with  the  main 
creek,  green  clays  containing  disseminated  crystals  of  magnetite  are 
found.  This  material  resembles  some  of  the  earthy  material  from 
the  mines,  and  with  little  doubt  it  represents  the  weathered  crop  of  a 
stratum  belonging  to  the  set  of  beds  which  carries  the  ore  deposits 


BULLETIN  NO.  359  PL.  VI 


GEOLOGIC  SKETCH  MAP  OF  VICINITY  OF  WHEATFIELD  MINES,  BERKS  COUNTY,  PA. 


BERKS  COUNTY  DEPOSITS. 


33 


H miles  to  the  east.  Appearances  also  favor  the  opinion  that  this 
horizon  is  nearly  the  same  as  that  of  the  ore-bearing  beds  at  slope 
Xo.  1 and  at  the  Ruth  mine.  Outcrops  of  Mesozoic  sandstone  are 
seen  on  the  east  bank  of  the  brook  near  by,  and  1,000  feet  or  so  up- 
stream red  shales  and  sandstones  are  present,  striking  X.  10°  E.  and 
dipping  30°  AY.  In  the  bed  of  the  eastern  brook  the  strike  is  the 
same,  but  the  dip  is  only  10°  AY. 

The  attitude  of  the  rocks  in  the  several  places  mentioned  above 
shows  that  there  is  g,  strong  unconformity  between  the  Mesozoic 
sandstone  and  the  set  of  strata  which  carries  the  ores;  this  is  also 
shown  by  the  fact  that  in  some  places  the  younger  beds  rest  directly 
upon  the  limestones,  whereas  in  others,  as  on  the  knoll  south  of  the 
Ruth  mine,  they  were  deposited  upon  the  stratigraphically  higher 
slate.  This  relation  makes  it  evident  that  none  of  the  rocks  which 
incase  the  ore  can  belong  to  the  Mesozoic,  though  the  contrary  was 
believed  to  be  the  case  by  Rogers,  whose  opinion  was  accepted  by 
AATllis,®  and  by  D’lnvilliers *  6 at  the  time  his  report  upon  the  geology 
of  Berks  County  was  written. 


A B 


Fig.  3. — East- west  structure  section  1,000  feet  south  of  public  road,  Wheatfield  group 
(along  line  C-C',  PI.  VI).  1,  Paleozoic  slate;  2,  Mesozoic  beds ; 3,  Paleozoic  lime- 
stone ; 4,  diabase  intrusion. 


The  rocks  in  the  neighborhood  of  the  AA7heatfield  group  of  mines 
are  sufficiently  exposed  to  reveal  very  complicated  geologic  relations 
without  being  well  enough  shown  t o make  possible  the  determination 
of  these  relations  in  detail.  Information  is  lacking  which  might 
suggest  the  shape  of  the  diabase  intrusion  underground  or  which 
might  lead  to  an  estimate  regarding  either  the  thickness  of  the  cal- 
careous beds  which  carry  the  ore  deposits  or  the  nature  of  the  strata 
which  lie  below  them.  All  these  points  must  be  known  in  at  least  a 
general  way  before  geologic  cross  sections  of  any  practical  value  can 
be  drawn.  The  sedimentary  rocks  of  the  area  which  sets  back  into 
the  main  dike  of  diabase  may  be  partly  or  entirely  underlain  by  a 
mass  of  igneous  rock  forming  a connection  between  the  main  cross- 
cutting dike  and  the  southerly  body  of  diabase,  or  it  may  be  that  the 
surrounding  masses  of  diabase  approach  each  other  only  at  rather 

a Willis,  Bailey,  Tenth  Census,  yol.  15,  p.  228. 

6 Second  Geol.  Survey  Pennsylvania,  Kept.  D3,  1883. 

54370— Bull.  350—08 3 


34 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


great  depth.  Whatever  the  actual  relations  may  be,  they  can  not  be 
made  out  from  features  observed  on  the  surface,  and  their  determina- 
tion must  await  information  furnished  by  diamond-drill  explorations. 

Systematic  study  of  the  Paleozoic  formations  of  the  district  might 
definitely  fix  the  position  of  the  Wheatfield  ore-bearing  strata  with 
reference  to  the  quartzite  which  occurs  in  the  ridge  just  north  of  the 
diabase  intrusion,  and  furnish  a basis  for  estimating  their  thickness 
in  the  vicinity  of  the  mines.  These  determinations  would  be,  how- 
ever, of  small  practical  value  compared  with  data  which  might  be 
procured  incidentally  if  a few  well-located  holes  were  drilled  to  test 
the  downward  extension  of  the  ore-bearing  strata  and  the  degree  to 
which  they  are  mineralized  in  depth. 

PRACTICAL  CONCLUSIONS. 

Though  so  much  is  indefinite  or  unknown  regarding  the  geology  of 
the  Wheatfield  deposits,  yet  the  number  and  distribution  of  the  ore 
beds  already  worked,  the  observable  structure  of  the  strata  in  which 
the  deposits  lie,  and  the  general  relations  which  they  bear  to  the  dia- 
base mass  and  the  overlying  Mesozoic  strata,  when  considered  to- 
gether, suggest  that  the  expense  of  a certain  amount  of  exploration  in 
the  northern  half  of  the  sedimentary  embayment  wrould  be  justified  by 
the  chances  of  locating  important  bodies  of  ore.  As  already  stated, 
the  impression  gained  from  strikes  and  dips  in  the  band  of  ore-bearing 
strata,  and  from  the  occurrence  of  the  twTo  patches  of  slate  at  the  Ruth 
mine  and  slope  No.  1,  is  that  the  strata  which  carry  the  ore  beds  in 
the  southern  group  of  mines  lie  stratigraphically  below  the  slate.  At 
the  Ruth  mine  the  slate  and  limestone  beds  lie  nearly  horizontal,  and 
it  seems  that  a hole  drilled  anywhere  between  this  old  opening  and  the 
first  northward-flowing  creek  to  the  east  must  penetrate  the  whole  set 
of  ore-bearing  beds  unless  part  of  them  are  cut  out  beneath  by  the 
intrusive  diabase.  The  proximity  of  the  diabase  would  lead  to  the 
expectation  that  beds  suitable  in  composition  for  impregnation  with 
iron  minerals  would  be,  in  part,  at  least,  converted  to  ore.  Southward 
from  the  Ruth  mine  the  limy  strata  are  overlain  at  first  by  slate  and 
finally  by  sandstone  as  well,  but  beneath  perhaps  150  feet  of  this  cap- 
ping they  doubtless  come  into  contact  with  the  cross-cutting  mass  of 
diabase  which  forms  the  bold  hills  west  of  the  wagon  road,  and  the 
vicinity  of  this  contact  is  again  favorable  to  the  presence  of  ore. 

It  is  probable  that  under  the  meadow  which  extends  along  the 
creek  the  set  of  ore-bearing  strata  would  be  encountered  immediately 
beneath  the  valley  wash,  as  indicated  by  the  beds  of  limestone  out- 
cropping between  the  two  northward-flowing  tributaries.  Further- 
more, the  southward  dip  of  the  diabase  wall  in  slope  No.  1 suggests 
that  these  strata  will  be  found  resting  upon  the  inclined  floor  of  the 


BERKS  COUNTY  DEPOSITS. 


35 


intrusive  rock  in  a manner  reproducing  in  a way  one  of  the  striking 
features  of  the  Cornwall  deposit. 

From  a practical  standpoint  deep  prospecting  in  the  vicinity  of  the 
main  workings  of  the  Wheatfield  group  would  seem  to  offer  somewhat 
better  chances  for  a successful  outcome  than  explorations  elsewhere 
in  the  neighborhood,  because  the  presence  of  ore  in  so  many  places 
reveals  the  fact  that  there  has  been  a very  important  amount  of  min- 
eralization. With  reference  to  the  theory  that  the  ores  of  the  Corn- 
wall type  have  been  produced  by  replacement  of  limy  strata  induced 
by  the  intrusive  diabase,  it  is  more  than  likely  that  the  mineralizing 
solutions  percolating  through  the  rocks  moved  away  from  the  hot  dia- 
base rather  than  toward  it  and  at  the  same  time  tended  mainly  up- 
ward toward  the  surface  rather  than  downward  toward  the  source 
of  heat. 

This  line  of  reasoning  leads  to  the  expectation  that  the  ore  bodies 
coming  to  the  surface  along  the  eastern  leg  of  the  band  of  Paleozoic 
strata  may  increase  in  number  as  well  as  in  size  and  persistency  as 
the  ore-bearing  strata  are  followed  downward  along  their  west  and 
southwest  dips. 

The  practical  question  whether  hard  iron  ores  of  the  grade  thus 
far  found  in  the  unweathered  portions  of  the  Wheatfield  deposits,  if 
discovered  in  comparatively  large  amount,  would  be  worth  developing 
at  the  present  time  lies  beyond  the  scope  of  the  present  investigation. 
The  writer  believes,  however,  that  the  fact  that  the  owners  have  never 
attempted  to  determine  the  real  possibilities  of  the  property  by  sys- 
tematic prospecting  can  not  be  taken  as  evidence  that  such  exploration 
is  not  fully  warranted  as  an  undertaking  likely  to  give  adequate 
returns  on  the  required  outlay. 

As  already  pointed  out,  the  Wheatfield  mines,  as  well  as  the  Fauden- 
busch  and  Island  mines,  which  lie  about  7 miles  to  the  east,  are  next 
to  the  same  mass  of  intrusive  diabase  at  the  only  localities  where  it 
comes  into  contact  with  the  Paleozoic  formations  on  the  surface  (Pis. 
V and  VI).  Throughout  the  interval  the  diabase  has  the  form  of  a 
northward-dipping  sill  outcropping  parallel  with  and  from  one-half 
to  1 mile  south  of  the  northern  edge  of  the  Mesozoic  belt.  Somewhere 
beneath  the  surface  the  sill  must  reach  the  Paleozoic  rocks  beneath 
the  cover  of  Mesozoic  shales  and  sandstones,  and  it  seems  very  likely 
that  here  its  form  changes  to  that  of  a dike.  If  this  be  the  case,  con- 
ditions favorable  for  the  occurrence  of  ore  may  exist  along  the  walls 
of  the  dike  wherever  limy  Paleozoic  strata  come  into  contact  with  it. 
Probably  the  most  favorable  condition  would  be  realized  if  strata 
which  correspond  in  stratigraphic  position  with  those  at  the  Wheat- 
field  mines  could  be  found  next  to  the  dike. 

Though  the  broad  suggestion  that  buried  ore  bodies  may  exist  in 
the  situation  indicated  seems  entirely  valid,  the  chances  of  locating 


36 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


deposits  of  value  are  regarded  as  too  remote  to  be  seriously  considered 
from  a practical  standpoint.  Prospecting  along  this  strip  of  country 
north  of  the  diabase  sill  is  therefore  not  recommended  except  where 
the  intrusion  approaches  the  northern  edge  of  the  Mesozoic  belt,  and 
even  here  the  possibilities  can  hardly  be  regarded  as  very  encouraging. 

For  2J  miles  east  of  Fritztown  station  the  diabase  is  in  contact  with 
Paleozoic  rocks,  but  beyond  the  fact  that  the  hills  north  of  the  diabase 
are  composed  of  quartzite  (in  one  place  dipping  50°  S.),  nothing 
concerning  the  local  geology  can  be  ‘stated  at  the  present  time,  because 
the  country  has  not  been  examined  in  detail.  If  limestone  beds  are 
present  above  the  quartzite,  and  if  the  general  dip  of  the  formations 
is  toward  the  south,  so  as  to  carry  them  down  beneath  the  diabase, 
the  vicinity  of  the  contact  would  seem  to  offer  favorable  conditions 
for  the  occurrence  of  ore  masses  like  those  which  are  present  imme- 
diately opposite,  on  the  south  side  of  the  dike. 

RAUDENBUSCH  MINE. 

Describing  the  Raudenbusch  property  in  1858,  H.  D.  Rogers  says : a 

About  balf  a mile  west  of  the  preceding  [Island  mine]  is  the  Raudenbusch 
mine,  which,  we  are  informed,  yields  its  proprietors  at  the  Phoenixville  furnaces 
5,000  tons  of  ore  per  annum.  The  vein  ranges  a little  north  of  east.  Its  foot 
wall  is  white  metamorphic  limestone,  or  marble,  and  its  hanging  wall  or  roof 
a dull  sea-green,  serpentine-like  rock  which  on  exposure  soon  crumbles  down 
like  ordinary  shale.  The  vein,  dipping  36°  S.,  is  followed  by  a slope  280  feet 
beneath  the  surface.  At  the  bottom  gangways  are  driven  200  feet  west  and 
400  feet  east  to  a fault  cutting  out  the  vein.  A higher  level,  160  feet  from  the 
surface,  is  driven  300  feet  east.  The  ore  is  now  taken?  from  this  level.  Like 
all  others,  this  vein  is  exceedingly  variable;  while  wholly  or  almost  entirely 
absent  in  some  places,  in  others  it  hfts  been  found  30  feet  thick.  Its  average 
bulk  will  not  exceed  12  feet.  The  gangue  stone  of  the  ore  is  a light-blue  rotten 
limestone,  from  which  the  ore  is  scarcely  distinguishable  except  by  its  greater 
weight  and  deeper  tint.  Of  the  entire  ground  wrought,  about  one-half  of  the 
material  is  sufficiently  rich  in  iron  for  the  furnace;  the  remaining  rubbish  is 
used  as  stopping  in  the  old  workings. 

D’Invilliers  states : 1 

There  are  two  small  shafts  on  the  property,  one  of  them  50  feet  deep.  On 
the  dump  are  seen  gray,  greenish,  and  black  limestones  very  much  decom- 
posed, some  of  which  may  represent  the  presence  of  the  brecciated  Mesozoic 
“ all  sorts  ” [i.  e.,  limestone  conglomerate]  so  characteristic  of  this  part  of  the 
range,  but  none  such  is  seen  in  place  on  the  surface.  * * * Most  of  the 
limestones  seem  altered,  which  is  accounted  for  by  the  proximity  of  the  trap 
dike  [diabase]  to  the  south.  This  trap  shows  in  the  50-foot  shaft,  as  also 
some  light-gray  to  white  limestone,  the  latter  showing  a slight  coating  of 
hematite. 


n Geology  of  Pennsylvania,  vol.  2,  1859,  pp.  716-717. 

0 Geology  of  Berks  County  : Second  Geol.  Survey  of  Pennsylvania,  Kept.  D3,  1883,  pp. 
342-343. 


BERKS  COUNTY  DEPOSITS. 


37 


To  the  present  writer  it  seems  unlikely  that  any  Mesozoic  rocks, 
either  limestone  conglomerates,  shales,  or  sandstones,  are  present 
north  of  the  diabase  in  this  vicinity.  The  only  rock  now  to  be  seen 
at  the  surface  is  white  limestone  exposed  in  the  farm  road  that  gives 
access  from  the  public  road  to  the  fields  just  north  of  the  old  mine. 
South  of  the  wagon  road,  on  the  slope  of  the  hill,  a shaft  not  men- 
tioned above  was  sunk  through  a green  shaly  rock,  probably  the  same 
as  that  referred  to  by  Rogers  as  forming  the  hanging  wall  of  the  ore. 
This  material  seems  to  be  of  sedimentary  origin,  and  it  evidently  lies 
between  the  ore  and  associated  limestone  beds  and  the  mass  of  diabase 
that  forms  the  adjacent  hill.  The  surface  distribution  of  the  diabase 
is  shown  on  the  sketch  map  (PI.  Y),  from  which  it  may  be  seen  that 
it  is  a northward  offshoot  from  the  intrusive  sill  described  in  the  dis- 
cussion of  the  Wheatfield  mines.  In  relation  to  the  Mesozoic  strata, 
this  northward-reaching  arm  is  evidently  crosscutting,  though  in 
respect  to  the  Paleozoic  strata  it  may  be  locally  following  the  bed- 
ding, as  is  suggested  by  the  southerly  inclination  of  the  old  mine 
slope. 

It  seems  a reasonable  conclusion  from  what  is  known  concerning 
the  distribution  of  quartzite,  slate,  and  limestone  along  the  south 
edge  of  the  Paleozoic  area  that  the  Raudenbusch  deposit,  like  those 
of  the  Wheatfield  group,  lies  in  the  beds  of  passage  between  the 
quartzite  and  the  limestone.  Crumpled  slate  is  exposed  in  a little 
knoll  about  1J  miles  southwest  of  the  mine  and  one-half  mile  west  of 
the  Center  Hotel;  just  west  of  this  knoll  quartzite  appears  with  dips 
toward  the  southeast  beneath  the  slate.  In  the  road-metal  quarry 
along  the  wagon  road  on  the  east  side  of  the  slate  knoll,  Mesozoic 
conglomerate  rests  upon  the  slate,  with  its  stratification  dipping 
gently  southward.  Half  a mile  east  of  the  mine  southward-dipping 
quartzite  forms  the  prominent  hill  south  of  the  reservoirs  above  the 
wagon  bridge  over  Angelic  Creek.  Immediately  south  of  this 
quartzite  knoll,  slates  and  limestones  may  come  in  above  the  quartz- 
ite before  the  diabase  is  reached,  but  their  presence  or  absence  can 
not  be  determined  because  of  the  existing  mantle  of  -surface  debris. 
It  is  suggested  that  other  ore  beds  like  the  one  formerly  mined  may 
exist  along  the  northern  wall  of  the  diabase  both  east  and  west  of  the 
Raudenbusch  mine.  On  the  west  the  question  could  be  readily  set- 
tled by  running  crosscut  tunnels  toward  the  diabase  and  drifting 
either  along  the  contact  or,  perhaps  better,  along  the  hanging  wall  of 
green  slate,  which  will  probably  be  encountered  before  the  intrusive 
rock  is  reached. 

Suggestions  for  prospecting  eastward  from  the  Raudenbusch  mine 
will  be  deferred  until  after  the  Island  mine  has  been  described. 


38 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


FRITZ  ISLAND  AND  VICINITY. 

ISLAND  MINE. 

The  Island  mine  is  situated  2 miles  south  of  Reading,  at  the  north 
end  of  Fritz  Island,  in  Schuylkill  River.  The  old  workings  are  very 
near  the  edge  of  the  Mesozoic  belt,  and  are  thought  to  have  pene- 
trated the  Paleozoic  limestone  which  lies  beneath  the  Mesozoic  strata. 
Large  masses  of  diabase  are  present  in  the  vicinity  and  dikes  of  the 
same  rock  were  encountered  in  the  mines  (PI.  V).  The  geologic 
features  of  the  mine  may  be  summarized  from  the  account  by  D’ln- 
villiers.® 

The  ore  was  encountered  through  the  washing  away  of  some 
ground  by  high  water  during  the  winter  of  1850-51.  In  opening  the 
mines  and  extending  the  workings  underground  it  was  found  that 
the  ore  occurs  in  a magnesian  limestone,  with  associated  shales  of  a 
sea-green  color  like  those  at  the  Raudenbusch  mine,  and  that  the 
ore-bearing  strata  are  capped  over  by  a limestone  conglomerate. 

Diabase  is  here  and  there  the  foot  wall,  but  beneath  the  ore  there 
is,  more  commonly,  a decomposed  sandstone,  regarded  as  of  Cam- 
brian age,  and  therefore  similar  to  the  quartzite  outcropping  in  the 
knoll  about  half  a mile  to  the  north.  The  ore  pinches  and  swells,  as 
in  the  Boyertown  mines,  the  maximum  recorded  thickness  being  22 
feet.  Horses  or  wedges  of  limestone  are  found  with  ore  occurring 
on  either  side.  The  strike  of  the  deposits  is  nearly  east  and  west, 
and  though  the  general  dip  seems  to  be  toward  the  north,  in  places 
at  an  angle  as  great  as  40°,  locally  the  ore  stands  vertical  or  even 
dips  toward  the  south.  Slope  No.  1,  beginning  on  the  outcrop,  is 
231  feet  deep,  being  inclined  at  the  top  about  62°  and  averaging 
about  46°.  Three  levels  were  run  eastward  from  the  slope,  passing 
under  the  bed  of  the  river  and  under  a small  island  in  the  eastern 
channel,  known  as  Yost  Island.  West  of  the  shaft  the  two  lower 
levels  were  carried  about  150  feet,  which  brought  them  beneath  the 
east  end  of  the  open  pit  (PL  VII).  The  gangways  are  about  60 
feet  apart,  the  upper  one  being  about  50  feet  below  the  surface. 

Considerable  stoping  was  done  above  the  lowest  level.  In  the 
bottom  of  the  mine,  125  feet  east  of  the  slope,  the  ore  was  found  to 
branch  and  was  followed  by  two  drifts  which  came  together  175  feet 
beyond.  Irregularity  of  dip  is  shown  by  the  vertical  attitude  of  the 
vein  in  the  middle  level  300  feet  east  of  the  slope.  Diabase  was  en- 
countered beneath  the  ore  in  all  the  drifts,  and  a crosscut  from  the 
bottom  level  revealed  a leader  of  ore  on  the  south  side  of  this  dike. 
The  dike  is  somewhat  more  than  100  feet  thick,  and  its  south  wall 
nearly  vertical.  The  ore  lying  south  of  the  dike  dips  to  the  south 
and  is  thought  to  be  the  same  vein  as  that  opened  by  slope  No.  2 and 


“ Second  Geol.  Survey  Pennsylvania,  Kept.  D3,  1883,  pp.  333-342. 


BULLETIN  NO.  350  PL.  VII 


MAP  OF  FRITZ  ISLAND  IRON  MINES,  BERKS  COUNTY,  PA. 


BERKS  COUNTY  DEPOSITS. 


39 


worked  to  a depth  of  about  100  feet  above  the  crosscut  from  slope 
No.  1.  The  position  of  slope  No.  2 is  about  300  feet  northwest  by 
Avest  from  No.  1. 

In  1883  slope  No.  2,  which  is  sunk  through  rock,  Avas  down  122 
feet  on  a dip  of  40°  to  55°,  averaging  perhaps  45°,  but  the  direction 
of  slope  is  not  stated. 

The  open-cut  workings  seem  to  have  had  considerable  importance, 
although.no  record  has  been  found  concerning  the  features  which 
they  exhibited.  The  old  pit  extends  east  and  Avest  and  is  nearly  300 
feet  in  length. 


NNW. 


SSE. 


Probable  fault 

West  Channel 


Gravel  bed 


PaleozoicWU^es'00  Ae, 


'//L  cOf'&  ,-f^-rv//  Llmeaiuiie  anu  sanuaivire 


aleozoic' 
Limestone  and  sandstone/ 


Fig  4. — Sketch  section  at  north  end  of  Fritz  Island. 


The  average  daily  production  of  the  mine  in  1883  Avas  25  to  30 
tons,  amounting  to  about  10,000  tons  per  year.  At  that  time  only 
one  slope,  No.  1,  Avas  being  operated.  The  total  yield  up  to  1883 
Avas  estimated  at  250,000  tons. 

The  general  relations  of  the  different  rocks  indicated  by  the  fore- 
going description  are  shown  in  fig.  4.  Apparently  there  is  a Avedge 
of  Paleozoic  limestone  lying  between  diabase  dikes  on  the  south  and 
northAvard  dipping  conglomerate  on  the  north,  but  it  is  not  known 
AAThether  the  ore  bodies  followed  the  bedding  of  the  inclosing  rocks 
or  not.  On  Fritz  Island  the  thin  edge  of  the  wredge  has  been  removed 


Fig.  5. — Sketch  section  along  river  bank  east  of  Fritz  Island  mines. 


by  erosion,  and  the  same  relation  probably  exists  near  the  towpath 
on  the  east  side  of  the  Schuylkill,  AAThere,  as  reported,  ore  was  discov- 
ered in  a prospect  shaft.  Farther  east,  however,  the  Paleozoic  rocks 
seem  to  be  capped  over  by  Mesozoic  strata  in  some  such  manner  as 
indicated  in  fig.  5.  In  the  two  figures  just  mentioned  a fault  is 
shoAvn  betAveen  the  Mesozoic  and  Paleozoic  areas,  because  the  north- 
erly dip  of  the  conglomerate  makes  it  difficult  to  see  Iioav  this  bound- 
ary could  be  formed  by  simple  overlap.  At  many  places  the  nature 
of  the  northern  boundary  of  the  Mesozoic  is  a vexing  question,  for 
though  overlap  is  locally  observable,  elsewdiere  there  is  strong  evi- 
dence of  fault  displacements  of  considerable  amount. 


40 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Future  mining  on  Fritz  Island  is  not  likely,  as  the  property  has 
been  acquired  by  the  city  of  Heading  to  be  used  as  a sewer  farm,  but 
even  if  otherwise  available  the  fact  that  the  old  workings  run  out  be- 
neath the  river  introduces  an  element  of  danger  from  flooding  which 
might  preclude  further  development.  From  a purely  geologic  stand- 
point it  seems  that  the  deposit  might  be  expected  to  show  considerable 
continuity  in  depth,  for  if  the  ore  beds  already  worked  are  not  actu- 
ally continuous,  others  might  be'discovered  by  deep  prospecting  along 
the  contacts  of  the  intrusive  masses  of  diabase. 

The  statement  is  made  in  the  report  b}7  D’Invilliers  * that  mining 
toward  the  east  was  discontinued  somewhere  beneath  Yost  Island 
because  of  poor  ventilation,  so  that  it  may  be  inferred  that  ore  still 
remains  at  this  place.  The  fact  that  ore  was  also  found  on  the  east 
side  of  the  river  near  the  towpath  is  a further  indication  favorable 
to  prospecting  in  this  direction.  The  rocks  which  have  furnished  the 
surface  debris  in  the  neighborhood  are  shales,  sandstones,  limestone 
conglomerate,  and  diabase,  and  the  ore-bearing  strata  can  hardly 
come  to  the  surface  except  in  a narrow  wedge-shaped  area  near  the 
river  bank.  As  the  northeast  wall  of  diabase  is  followed  in  a south- 
easterly direction,  the  limestones  are  found  to  become  covered  by  a 
rapidly  thickening  cap  of  the  younger  strata,  so  that  it  seems  that  any 
ore  bodies  existing  will  be  found  to  lie  deeper  and  deeper  toward  the 
southeast.  In  making  the  above  suggestion  it  is  assumed,  as  else- 
where in  this  report,  that  ore  will  not  occur  except  near  the  intrusive 
rock,  and  that  important  bodies  are  not  likely  to  be  found  where  the 
diabase  is  in  contact  with  other  than  calcareous  strata.  The  only  ex- 
ception to  this  rule  which  has  been  noted  is  at  Boyertown,  where  the 
Black  vein  and  the  East  vein  are  both  some  distance  away  from  the 
diabase  intrusion. 


EAST  BANK  OF  SCHUYLKILL  RIVER. 

On  the  east  side  of  the  Schuylkill,  as  on  Fritz  Island,  the  diabase 
is  not  a solid  mass,  twTo  dikes  being  separated  from  the  main  body 
lying  to  the  south  by  strips  of  Mesozoic  shale.  If  these  dikes  continue 
downward  and  penetrate  the  ore-bearing  limestones  separately,  cross- 
cut tunnels  would  seem  to  be  justified  in  order  to  explore  all  their 
walls,  and  also  that  of  the  larger  intrusive  mass  beyond.  This  sup- 
position is  suggested  by  the  occurrence  of  ore  on  both  sides  of  the  100- 
foot  dike  in' the  Island  mine. 

It  would  seem  that  if  due  care  is  taken  to  avoid  breaking  into  the 
old  Island  mine  workings,  further  prospecting  from  the  east  side 
of  the  river  will  be  warranted  by  the  probability  of  finding  ore 
bodies  similar  to  those  formerly  worked  on  Fritz  Island.  The  known 


Second  Geol.  Survey  Pennsylvania,  Rept.  D3,  1883,  pp.  337-338. 


BERKS  COUNTY  DEPOSITS. 


41 


presence  of  ore  near  the  river  bank  would  apparently  justify  a shaft, 
from  which  tunnels  could  be  run  as  suggested  above.  Prospecting 
m this  manner  would  probably  be  more  satisfactory  than  by  a series 
of  drill  holes. 

WEST  BANK  OF  SCHUYLKILL  RIVER. 

West  of  the  river  the  presence  of  deep  surface  wash  makes  it  im- 
possible to  determine  whether  the  fields  below  the  wagon  road  are 
underlain  entirely  by  diabase  or  in  part  by  sedimentary  rocks  Efia- 
base  is  exposed  opposite  the  north  end  of  Fritz  Island,  but  from 
the  existence  of  two  outlying  dikes  east  of  the  river  and  at  least  one 
on  the  island,  all  with  apparently  east-west  courses,  it  may  very 
well  be  that  this  outcrop  belongs  to  a mass  lying  north  of  the  main 
intrusion.  The  question  whether  this  is  so  or  not  is  important  and 
could  be  settled  at  slight  cost  by  running  two  or  three  short  tunnels 
from  the  bank  of  the  western  channel  above  the  Fritz  Island  bridge. 
It  is  believed  that  if  any  other  rock  than  diabase  is  found  there  would 
be  a good  chance  of  discovering  ore  bodies  like  those  of  the  Island 
mine  by  systematic  prospecting.  It  is  perhaps  not  likely  that  lime- 
stone conglomerate  will  be  encountered,  but  if  it  should  be  present 
it  would  only  be  necessary  to  turn  northward  and  penetrate  this  cap 
in  order  to  reach  the  Paleozoic  strata.  If  any  ore  should  be  found 
it  would  be  desirable  to  determine  how  many  outyling  dikes  of 
diabase  exist  and  to  explore  carefully  all  contacts. 

ESTERLY  MINE. 

About  4 miles  due  east  of  the  Fritz  Island  mine  and  2 miles  south 
of  Jacksonwald,  on  the  W.  Esterly  farm,  a small  deposit  of  mag- 
netite was  once  worked.  William  G.  Rowe,  of  Reading,  is  authority 
for  the  statement  that  this  mine  furnished  between  3,000  and  4,000 
tons  of  ore.  It  was  opened  to  a depth  of  125  feet  by  a 58°  slope  in- 
clined toward  the  north,  the  drifts  being  run  about  250  feet  to  the 
east.  About  600  feet  southeast  of  the  Esterly  slope  an  opening 
known  as  the  Bishop  shaft  was  sunk  for  150  feet  and  a north  cross- 
cut driven  for  200  feet,  ending  in  garnet  rock.  A bore  hole  from 
the  bottom  of  this  shaft  reached  limestone  conglomerate  at  about 
300  feet. 

The  Esterly  vein  lies  between  a hanging  wall  of  diabase  and  a foot 
wall  of  metamorphosed  shale.  The  diabase  is  an  intrusive  sill  in- 
cluded in  northward- dipping  strata.  In  the  neighborhood  of  the 
intruded  rock  there  has  been  considerable  baking,  and  here  and  there 
such  metamorphic  minerals  as  garnet,  hornblende,  and  magnetite  are 
found.  These  minerals,  with  some  chlorite,  are  present  in  the  ma- 
terial on  the  old  mine  dump,  and  the  silicates  evidently  occur  in 
close  association  with  the  magnetite  of  the  ore.  Some  limy  material 


42 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


is  to  be  noted,  but-  no  pure  limestone ; it  seems,  therefore,  that  this 
ore  was  formed  by  the  replacement  of  shales  under  the  mineralizing 
influence  of  the  diabase. 

The  diabase  is  the  outer  of  two  concentric  curving  sills  which  fol- 
low the  bedding  of  the  Mesozoic  shales  and  sandstones,  here  throAvn 
into  a rather  sharp  synclinal  fold  (PI.  V).  The  ore  bed  lies  on  the 
lower  contact  of  the  sill  and,  like  it,  strikes  conformably  with  the  in- 
closing rocks,  nearly  east  and  west,  with  a dip  of  about  50°  N.  The 
deposit  may  be  imagined  to  have  considerable  downward  extent, 
though  of  course  its  continuity  in  this  direction  can  not  be  affirmed. 
Along  the  strike  it  is  rather  short,  as  not  more  than  100  feet  west  of 
the  slope  carbonaceous  and  limy  shale  is  exposed  along  the  road,  and 
though  the  situation  is  very  near  the  diabase  contact  no  magnetite 
has  been  developed. 

No  other  magnetite  is  known  to  have  been  found  along  either  side 
of  this  arm  of  the  sill,  but  Mr.  Rowe  states  that  specimens  have  been 
plowed  up  in  the  fields  near  Spring  Creek,  between  the  northern 
arm  and  Stonersville.  Though  some  prospecting  was  done  in  this 
vicinity,  no  magnetite  was  found  in  bed  rock.  It  is  possible  that  the 
mineral  may  have  been  float  from  a deposit  situated  near  the  diabase 
wall  on  the  hill  slopes  above  the  creek,  though  it  may  have  been  de- 
rived from  a pocket  lying  in  the  limestone  conglomerate  which  covers 
considerable  ground  on  the  west  side  of  Spring  Creek  south  of  the 
Reading  turnpike. 

In  this  place  the  strata  of  limestone  conglomerate  dip  rather 
steeply  to  the  southwest.  This  dip  would  carry  them  beneath  the 
diabase  sill,  but  the  outcrops  are  so  far  from  those  of  the  diabase 
that  it  seems  hardly  likely  that  any  important  body  of  ore  wTill  be 
found  in  this  rock,  at  least  near  the  surface.  In  depth  the  conglom- 
erates may  be  cut.  by  the  diabase,  and  if  so  there  would  be  a chance 
for  ore  bodies  in  them  and  likewise  for  the  occurrence  of  pockets  at 
some  distance  from  the  intrusive  rock. 

On  the  surface  shales  probably  come  between  the  conglomerate 
strata  and  the  diabase,  as  they  do  in  the  vicinity  of  the  Esterly  mine, 
though  the  hill  slope  above  Spring  Creek  on  the  south,  and  next  to 
the  conglomerate  outcrops  farther  north,  is  hidden  by  an  unbroken 
mantle  of  soil  and  diabase  fragments.  In  the  fields  above  the  wagon 
road,  however,  the  position  of  the  diabase  wall  may  be  closety  esti- 
mated from  the  presence  of  a sharp  rise  in  the  profile  of  the  hill,  and 
the  contact  could  be  reached  almost  anywhere  by  short  tunnels. 

In  view  of  the  fact  that  only  limestone  beds  have  thus  far  been 
found  to  yield  really  important  ore  deposits  of  the  Cornwall  type, 
it  can  not  be  urged  that  this  contact  is  a particularly  favorable  place 
for  prospecting,  though  it  is  undoubtedly  the  most  likely  place  for  ore 
occurrence  in  the  neighborhood.  No  general  recommendation  that  the 


BERKS  COUNTY  DEPOSITS. 


43 


diabase  contacts  should  be  prospected  through  their  entire  length 
seems  warranted,  though  the  discovery  of  ore  at  any  locality  would 
naturally  lead  to  a rather  careful  search  at  other  points. 

Both  arms  of  the  twTo  horseshoe  dikes  closely  approach  and  prob- 
ably actually  reach  the  northern  edge  of  the  Mesozoic  area,  and  inas- 
much as  limestone  occurs  everywhere  north  of  the  boundary  it  would 
seem  that  ore  bodies  might  be  expected  at  the  localities  where  the 
diabase  and  limestone  come  together.  It  is  believed,  however,  that  the 
diabase  does  not  intrude  the  limestone  at  any  of  these  places,  but  in- 
stead that  the  Paleozoic  and  Mesozoic  rocks  come  together  along  a 
fault  which  has  developed  since  the  younger  strata  in  the  synclinal 
fold  were  invaded  by  the  two  sills  of  diabase. 

BOYERTOWN  DEPOSITS. 

GENERAL  DESCRIPTION. 

The  mining  operations  which  have  been  carried  on  at  Boyertown 
have  developed  the  existence  of  five  apparently  separate  bodies  of 
magnetic  iron  ore,  all  of  which  exhibit  the  form  of  somewhat  irreg- 
ular layers  of  varying  thickness.  These  ore  layers  seem  to  follow 
rather  closely  the  stratification  of  a set  of  limestones  and  limy  shales 
which  constitute  a transition  between  “ No.  I ” sandstone  and  “ No. 
II  ” limestone  of  the  Paleozoic  section,  as  given  in  the  publications  of 
the  Second  Geological  Survey  of  Pennsylvania.  In  stratigraphic 
position  these  beds  correspond  with  the  ore-bearing  strata  at  the 
Wheatfield  and  Fritz  Island  mines. 

The  mine  openings  are  situated  near  the  northwest  edge  of  the 
Mesozoic  belt,  and  the  workings  have  shown  that  the  three  best- 
developed  ore  bodies  lie  immediately  beneath  a Mesozoic  basal  con- 
glomerate composed  of  limestone  fragments  up  to  an  inch  in  diameter 
set  in  a paste  of  red  clay.  This  conglomerate  bed,  with  a generai 
southwest-northeast  strike,  dips  toward  the  southeast,  and  beneath 
it  the  Paleozoic  strata  are  so  tilted  that  they  lie  in  nearly  parallel 
position.  The  two  other  ore  bodies  occur  well  within  the  limy  beds 
of  the  Paleozoic  at  contact  of  a mass  of  intrusive  diabase  (PI.  VIII). 
The  ore  bodies  just  beneath  the  conglomerate  are  here  called  the  East 
vein,  the  Hagy  (sometimes  known  as  the  Eckert)  vein,  and  the  War- 
wick or  Black  vein.  The  deposits  in  contact  with  the  diabase  are 
known  as  the  Rhoades  and  Blue  veins.  The  East  vein  was  worked 
from  two  inclined  shafts  situated  southeast  of  Walnut  street  and 
knowif  as  Phoenix  upper  and  middle  slopes.  The  Hagy  vein,  out- 
cropping south  of  the  Reading  road  in  the  outskirts  of  town,  was 
first  wmrked  by  means  of  an  open  excavation  known  as  the  Hagy  pit, 
afterwards  by  the  so-called  Eckert  slope,  and  finally  by  the  lower 
Phoenix  or  California  slope.  The  Warwick  vein  has  been  worked 


44  MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 

both  from  the  Warwick  shaft  and  from  the  two  shafts  of  the  Gabel 
mine.  In  the  latter  mine  it  was  called  the  Black  vein.  A body  of 
ore  ecountered  in  the  lower  workings  of  the  California  mine  and 
known  as  ore  No.  2 is  believed  by  the  writer  to  represent  the  north- 
ward extension  of  the  Warwick  vein.  The  Blue  vein  has  been  found 
only  in  the  Gabel  mine.  The  Rhoades  vein  has  been  opened  from  the 
surface  at  several  places  and  also  by  means  of  two  tunnels  from  the 
California  slope. 

It  is  suspected  that  connection  may  eventually  be  established  be- 
tween the  Blue  and  Rhoades  veins,  also  that  the  Warwick  and  Hagy 
veins  are  parts  of  a once  continuous  ore  body  separated  by  a fault. 
These  points  and  the  possible  relation  between  the  East  vein  and 
the  Hagy  vein  are  discussed  on  pages  58-60.  The  relative  positions  of 
the  several  mines  are  indicated  on  the  map  (PI.  VIII). 

The  strata  which  carry  the  deposits  occur  in  a narrow  strip  lying 
between  the  region  of  gneisses  and  sandstones  northwest  of  Boyer- 
town  and  the  Mesozoic  area  on  the  southeast.  The  length  of  this 
strip  is  at  least  2 miles  and ' possibly  somewhat  more,  but  all  the 
known  ore  bodies  occur  within  a distance  of  less  than  half  a mile. 

The  situation  of  the  deposits  with  respect  to  the  Mesozoic  rocks  is 
similar  to  that  of  the  Cornwall,  Wheatfield,  and  Fritz  Island  de- 
posits. Like  all  of  these,  they  are  associated  with  intrusive  diabase, 
and  though  this  association  is  somewhat  less  obvious  at  Boyertown 
than  elsewhere  it  is  sufficiently  evident  to  justify  the  conclusion  that 
the  ores  have  been  formed  under  the  influence  of  the  invading  rock, 
as  at  Cornwall  and  other  localities  where  ores  of  a similar  type  occur. 

GEOLOGY  OF  THE  DISTRICT. 

Boyertown  is  situated  near  the  northwest  end  of  a roughly  oval 
valley,  9 miles  long  from  southeast  to  northwest,  and  about  5 miles 
wide.  Ridges  formed  either  by  diabase  sills  or  by  sandstones  and 
shales  baked  and  hardened  by  the  intrusive  rock  define  this  valley 
on  three  sides,  the  remaining  or  northwest  side  being  formed  by  the 
Reading  Hills,  which  are  composed  mainly  of  ancient  gneisses,  but 
contain  also  limestones  and  quartzites.  From  the  ridges  the  strata 
dip  toward  the  interior  of  the  valley,  which  is  thus  structurally,  as 
well  as  topographically,  a broad  basin.  It  is  one  link  in  a chain  of 
four  similar  basins  that  extend  nearly  to  Delaware  River.  Each  of 
these  basins  is  rimmed  by  diabase,  the  outcrops  of  which  are  nearly,  if 
not  actually,  continuous.  The  great  extent  of  the  diabase,  the  con- 
tinuity of  its  outcrop,  and  the  persistency  with  which  the  infrusive 
rock  follows  the  structure  of  the  inclosing  strata  lead  to  the  belief 
that  it  forms  a practically  unbroken  sheet  beneath  all  the  basins  that 
are  surrounded  by  its  outcrop.  The  basin  here  discussed  is  not  com- 


GEOLOGICAL  SURVEY 


SURFACE  MAP  OF  BOYERTOWN  MINES,  SHOWING  RELATIVE  POSITION  OF  ORE  BODIES  ON  LEVEL  SURFACE  400  FEET  BELOW  TOP  OF 

GABEL  NO.  1 SHAFT. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  359  PL.  IX 


lxnile 


GEOLOGIC  SKETCH  MAP  OF  VICINITY  OF  BOYERTOWN,  BERKS  COUNTY,  PA. 


BERKS  COUNTY  DEPOSITS. 


45 


pletely  rimmed  by  the  igneous  rock,  but  it  seems  probable  that  the 
two  existing  gaps,  one  near  Boyertown  and  the  other  3 miles  to  the 
northeast  (PI.  IX  and  fig.  10),  are  to  be  explained  on  the  supposition 
that  in  these  places  the  invading  rock  was  not  able  to  force  its  way 
far  enough  upward  to  reach  the  present  surface  of  the  land. 

Just  south  of  the  mines  the  western  slope  of  Gabel  Hill  is  formed 
by  diabase,  which  marks  the  northward  termination  of  a curving  mass 
of  intrusive  rock  that  follows  the  base  of  the  ridge  and  the  valley  of 
Ironstone  Creek  to  Colebrookdale  station  and  farther  south  con- 
nects with  the  rim-rock  sills  on  the  southwest  side  of  the  synclinal 
basin  described  above.  The  sedimentary  rocks  adjacent  to  this  diabase 
have  been  greatly  metamorphosed,  and  Gabel  Hill,  together  with  the 
ridge  running  southward  from  it,  has  been  preserved  from  erosion 
by  the  indurated  nature  of  the  shales  and  sandstones  of  which  they 
are  composed.  The  originally  red  sandstones  have  been  bleached  to 
a dull  white  or  yellow.  A few  outcrops  suffice  to  show  that  the  strata 
strike  parallel  with  the  course  of  the  sill  and  with  the  crest  of  the 
ridge  and  dip  to  the  east  and  southeast  toward  the  interior  of  the 
basin.  North  and  east  of  the  blunt  end  of  the  diabase  outcrop  a few 
exposures  of  sandstone  have  the  natural  red  color  of  the  Mesozoic 
strata  and  show  no  induration.  In  the  Warwick  mine,  however,  and 
in  both  shafts  of  the  Gabel  mine  limestone  conglomerate  lying  above 
the  black  ore  is  somewhat  metamorphosed,  garnet  and  hematite  being 
developed  in  it.  These  minerals  occur  also  in  bowlders  both  of  lime- 
stone and  siliceous  conglomerate  on  Gabel  Hill.  The  surface  dis- 
tribution of  the  metamorphic  effects  conforms  so  closely  with  the 
extent  of  the  diabase  that  the  presence  of  common  metamorphic 
minerals  in  the  conglomerate  that  occurs  in  the  mines  points  definitely 
to  the  presence  of  intrusive  rock  near  by.  To  judge,  however,  from 
the  descriptions  of  D’Invilliers  ° and  Willis*  & the  instrusive  rock  is 
absent  from  most  parts  of  the  mines.  Small  dikes  were  noted  in  the 
Warwick  mine  and  diabase  is  known  to  lie  beneath  the  Rhoades  vein 
and  in  the  Gabel  No.  1 workings  beneath  the  Blue  vein.  Willis  shows 
this  rock  as  the  foot  wall  of  both  the  last-named  veins,  and  indicates 
its  presence  in  the  crosscut  tunnel  from  the  496- foot  level  of  the  War- 
wick mine,  which  was  opened  in  search  of  the  Blue  vein.  It  is 
thought  probable  that  a rather  direct  underground  connection  may 
exist  between  the  Gabel  Hill  deposits  near  Boyertown  and  the  masses 
of  the  same  rock  occurring  northeast  of  New  Berlinville,  and  also  be- 
tween the  latter  and  the  diabase  that  outcrops  east  of  Sassamansville. 

From  scattered  exposures  strata  corresponding  with  those  which 
carry  the  ore  layers  are  known  to  extend  about  one-half  mile  south- 


0 Second  Geol.  Survey  Pennsylvania,  Kept.  D3,  vol.  2,  pt.  1,  1883. 

6 Tenth  Census,  vol.  15,  1886. 


46 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


west  and  1 mile  northeast  of  the  mines,  and  they  may  continue  con- 
siderably farther  north  beyond  New  Berlinville,  beneath  the  alluvial 
wash  of  the  swampy  lands  along  the  railroad.  Shales  including  a 
dark  carbonaceous  layer  have  been  revealed  by  an  old  pit  in  a field 
between  the  Reading  turnpike  and  the  railroad  about  half  a mile 
north  of  the  California  slope,  and  shales  broken  down  by  surface 
weathering  are  exposed  on  both  sides  of  the  same  road  just  where 
the  trolley  track  leaves  it  and  turns  up  the  valley  of  Ironstone  Creek. 
Decomposed  shale  was  revealed  in  excavations  for  cellars  made  in 
1906  on  the  south  side  of  the  road  between  the  exposures  last  men- 
tioned and  the  engine  house  at  the  California  mine,  and  a few  lumps 
of  iron  ore  were  found  mixed  with  the  clay.  This  material  was 
apparently  undisturbed,  though  it  is  possible  that  it  may  have  been 
waste  from  the  mines.  A prospecting  shaft  situated  between  500 
and  600  feet  northeast  of  Philadelphia  avenue  along  the  strike  of 
the  East  vein  showed  the  presence  of  carbonaceous  shale  which  is 
reported  to  have  been  similar  to  some  of  the  material  associated  with 
the  ore,  and  which  very  likely  represents  the  ore  horizon,  as  the  lime- 
stone conglomerate  occurs  near  by.  Fragments  of  similar  limy  and 
carbonaceous  shale  containing  a little  pyrite  which  came  from  a 
slope  half  a mile  farther  northeast,  on  the  east  side  of  the  railroad 
track  opposite  the  clay  pit  and  brick  kilns,  may  still  be  found  scat- 
tered over  the  field.  A hole  was  drilled  near  by,  but  no  details  of 
this  prospecting  have  been  obtained.  The  clay  used  in  the  brick 
works  near  New  Berlinville  station  is  weathered  shale,  and  in  places 
where  the  decomposition  is  not  complete  the  rock  closely  resembles 
that  which  outcrops  southwest  of  the  California  mine  along  the 
Reading  turnpike.  North  of  New  Berlinville  no  exposure  of  shale 
has  been  noted,  though  it  probably  occurs  west  of  the  railroad  be- 
tween the  track  and  the  narrow  band  of  quartzite  that  is  represented 
on  the  geologic  map  of  the  Reading  and  Durham  hills  accompanying 
the  Berks  County  report  by  DTnvilliers.  From  the  mines  northeast- 
ward to  New  Berlinville  the  shales  and  accompanying  limy  beds  are 
overlapped  by  the  Mesozoic  strata,  the  strike  of  which,  though  vari- 
able from  place  to  place,  runs  in  general  nearly  parallel  with  the 
strip  of  Paleozoic  rocks.  The  dip  in  both  sets  of  rocks  is  toward  the 
southeast  and,  as  already  noted,  the  strata  lie  nearly  parallel.  From 
the  Rhoades  mine  toward  the  southwest  the  diabase  sill  appears  to 
separate  the  strata  of  the  ore-bearing  group  from  those  of  the 
Mesozoic  almost  as  far  as  the  Gresh  limestone  quarry,  a short  dis- 
tance east  of  which  the  sill  turns  southward  into  the  Mesozoic  area. 
At  the  quarry  baked  Mesozoic  shales  are  seen  almost  in  contact  with 
the  massive  blue  Paleozoic  limestone.  The  hill  above  the  quarry  is 
covered  with  fragments  of  whitened  and  indurated  sandstone. 


CO 


GENERAL  PLAN  OF  WORKINGS  AT  BOYERTOWN  MINES,  BERKS  COUNTY, 


BULLETIN  NO.  359  PL.  XI 


U.  S.  GEOLOGICAL  SURVEY 


B 

Gabel  No.  2 shaft 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO:  359  PL.  XI 


B 

Gabel  No.  1 shaft  Surface  Gabei  No-  2 shaft 


CROSS  SECTION  AT  BOYERTOWN  MINES  (ALONG  LINE  A-B,  PL.  X). 


BERKS  COUNTY  DEPOSITS. 


47 


THE  WORKINGS. 

All  the  mines  of  the  Boyertown  group  were  flooded  when  the  writer 
visited  the  locality,  and  for  this  reason  no  first-hand  information  con- 
cerning the  underground  geology  of  the  ore  deposits  enters  into  the 
present  descriptions.  The  facts  available  in  regard  to  the  geology  of 
the  mines  are  those  recorded  by  Willis  and  D’lnvilliers,  whose  descrip- 
tions are  quoted  below.  For  the  map  of  the  workings  which  forms 
PI.  X acknowledgment  is  due  the  former  engineer  and  superintendent 
of  the  Phoenix  mines,  Mr.  J.  H.  Harden,  of  Phoenixville,  by  whom 
it  was  in  part  drawn  from  original  surveys  and  in  part  compiled  from 
data  furnished  by  the  several  companies  which  formerly  owned  the 
mines.  The  workings  of  the  640-foot  level  of  Gabel  shaft  Xo.  2 have 
been  added  to  Mr.  Harden’s  map  from  notes  of  a survey  in  posses- 
sion of  W.  H.  Dechant,  successor  to  the  practice  of  Kendall  Brothers, 
civil  engineers,  formerly  located  at  Reading.  The  cross  sections  of 
the  mines  (Pis.  XI-XY)  have  been  constructed  from  the  data  afforded 
by  the  mine  maps,  with  the  aid  of  sketches  made  by  Mr.  Harden. 
Their  purpose  is  to  show  the  general  attitude  of  the  veins,  and  they 
do  not  take  account  of  the  many  existing  irregularities  of  thickness. 

DESCRIPTIONS  BY  WILLIS.0 

The  Phoenix  mines  present  the  simplest  structure.  Two  inclines,  having  an 
average  slope  of  46°,  are  sunk  on  the  ore,  between  a hanging  wall  of  Mesozoic 
red  sandstone  and  a foot  wall  of  dark-gray  limestone.  Drifts  * * * have 
been  driven  off  on  either  side  of  the  incline  and  the  ore  removed  by  stoping. 
The  bed  varies  from  7 to  12  feet  in  thickness,  and  near  the  hanging  wall  there 
is  usually  a selvage  of  chloritic  slate,  which  comes  down  in  mining.  The  strike 
is  quite  regular,  about  northeast  and  southwest,  and  the  beds  have  the  apparent 
prospect  of  continuing  indefinitely  in  either  direction ; just  southwest  of  the 
lower  incline  the  bed  is  pinched  out,  however,  and  no  exploration  has  been  made 
to  ascertain  whether  it  continues  or  not. 

A shaft,  known  as  Eckert’s,  * * * was  sunk  a short  distance  northeast  of 

the  California  incline,  and  “ Eckert’s  vein  ” was  opened  by  it.  The  Phoenix  com- 
pany owns  part  of  the  mineral  right  on  this  “ vein,”  and  the  California  incline 
was  sunk  through  rock  to  develop  it  and  “ Rhoades’s  vein,”  which  was  known 
by  surface  workings. 

* * * The  northeast  drifts  of  the  California  mine  reach  the  southwest  end 

of  Eckert’s  ore,  while  two  long  crosscuts  have  been  driven  through  limestone  to 
Rhoades’s  deposits.  Eckert’s  is  like  the  Phoenix  in  geological  relations,  but 
strikes  nearly  north  and  south,  with  a dip  to  the  east. 

Rhoades’s  vein  strikes  at  right  angles  to  the  Phoenix,  southeast  and  north- 
west, and  dips  northeast ; it  has  a hanging  wall  of  limestone  and  foot  wall  of 
trap,  and  in  this  resembles  the  deposit  opened  by  the  Gabel  shaft  [Blue  vein]  ; 
the  ores  obtained  from  the  two  openings  are  also  very  similar,  and  the  differ- 
ences of  strike  and  dip  are  hardly  sufficient  in  so  disturbed  a corner  to  render  it 
improbable  that  they  belong  to  the  same  deposit. 

a Tenth  Census,  vol.  15,  1886,  pp.  229-231. 


48 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


The  lowest  working  in  the  California  mine,  on  Eckert’s  vein,  is  218  feet  from 
the  surface  at  the  top  of  the  incline;  the  dip  is  about  45°  toward  the  east.  This 
drift  is  240  feet  from  the  Warwick  shaft,  measured  on  the  map.  Ore  was  first 
struck  in  that  shaft  at  a depth  of  about  400  feet,  probably  425  feet  below  the 
top  of  the  California  incline. 

A dip  of  38°  to  40°  would  place  a southern  extension  of  Eckert’s  vein  in  the 
position  of  the  ore  cut  in  the  Warwick  shaft.  It  does  not  follow  that  the  ore 
body  is  continuous  from  the  Warwick  workings  up  to  the  California  drifts. 
In  fact,  the  trap  which  lies  west  of  the  Warwick  shaft  and  that  penetrated  in 
the  long  crosscut  toward  the  Gabel  mine  render  it  very  improbable  that  there 
is  an  undisturbed  body  of  ore  here;  but  it  does  seem  probable  that  the  War- 
wick, the  Eckert,  and  perhaps  the  Phoenix  beds,  which  all  have  a red-sandstone 
hanging  wall  and  a limestone  foot  wall,  are  disturbed  portions  of  the  same 
originally  connected  bed. 


Fig.  6.  Plan  of  upper  or  496-foot  level,  Warwick  mine,  after  Willis.  1,  Diabase ; 2,  Meso- 
zoic sandstone  ; 3,  limestone  ; 4,  limestone  mixed  with  ore  ; 5,  magnetite  ore. 

A special  map  is  herewith  given  of  the  Warwick  mine  [fig.  6].  It  is  opened 
in  the  most  disturbed  portion  of  the  belt,  and  the  apparent  development  of  two 
parallel  ore  beds,  together  with  the  exceptional  facilities  afforded  by  the  kind- 
ness of  Captain  Polkinhorn,  led  to  careful  study  of  it.  In  the  long  drift  on 
the  middle  level,  toward  the  south,  there-  is  a well-defined  limestone  foot  wall. 
The  hanging  wall  of  red  sandstone  is  also  uninterrupted;  but  between  the  two, 
and  especially  in  the  northern  end  of  the  mine,  the  limits  of  the  ore  are  very 
ill  defined.  The  wall  is  usually  mixed  limestone  and  ore,  and  mining  is  left 
off  simply  when  the  proportion  of  ore  to  limestone  becomes  too  small  to  pay. 

Where  the  ore  body  turns  southward  the  upper  bed  of  ore  approaches  the 
lower  bed,  and  it  will  probably  be  found  that  there  is  but  one  extending  south- 
eastward beyond  the  next  turn  in  the  Gabel  property.  The  variations  in  the 
thickness  of  the  ore  bed  and  the  positions  of  the  associated  limestone,  red  sand- 
stone, and  trap  are  given  in  the  accompanying  special  map. 


u.  S.  GEOLOGICAL  SURVEY 

c 


CROSS  SECTiq 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  359  PL.  XII 


c 


100  a 100 200  feet 


CROSS  SECTION  AT  BOYERTOWN  MINES  (ALONG  LINE  C-D,  PL.  X). 


BERKS  COUNTY  DEPOSITS. 


49 


Accepting  the  inference  that  the  Warwick,  Eckert,  and  Phoenix  deposits  have 
originally  formed  parts  of  one  bed,  though  now  disturbed  and  separated  by 
“pinches,”  it  is  difficult  to  understand  how  the  Blue  (Gabel)  vein  and  the 
Rhoades  vein  can  ever  have  been  part  of  that  bed. 

The  foot  wall  of  the  Phoenix  and  the  Eckert  mines  is  apparently  tilted,  but 
otherwise  a little-disturbed  and  continuous  stratum.  Away  from  the  trap, 
which  has  confused  the  deposit  near  the  Warwick  shaft,  the  limestone  foot  wall 
is  in  that  mine  also  well  defined.  The  long  cut  driven  from  the  Gabel  bed  to 
the  large  deposit  in  the  south  end  of  the  Warwick  mine  passes  through  175 
feet  of  limestone.  The  same  material  lies  uninterruptedly  between  the  Eckert 
and  the  Rhoades  beds.  Hence  it  seems  highly  probable  that  there  are  here  two 
distinct  deposits  of  ore.  With  this  in  view,  it  would  be  interesting  to  know  the 
results  of  exploration  north  of  the  Phoenix  mines. 

DESCRIPTIONS  BY  DTnVILLIERS. 

The  following  descriptions  of  the  several  mines  are  abridged  from 
D’Invilliers’s  account  of  the  Boyertown  mines : 

Phoenix  upper  and  middle  slopes .a — These  slopes  are  850  feet  apart 
and  both  work  the  same  body  of  ore,  averaging  from  12  to  15  feet 
in  thickness,  though  at  many  places  swelling  into  bunches  three  times 
as  large  in  different  portions  of  the  different  gangways.  The  dip 
of  the  ore  averages  about  45°-SE.  The  upper  slope  is  853  feet  deep, 
vertical  measurement,  its  top  being  located  6 feet  higher  than  Gabel 
shaft  No.  1.  The  lowest  drift  is  driven  on  this  slope  from  the  bot- 
tom for  about  150  feet  each  way  northeast  and  southwest,  but  the 
courses  have  never  been  surveyed,  and  consequently  could  not  be 
located.  Forty-three  feet  vertically  above  this  is  the  middle  drift, 
likewise  driven  each  side  of  the  slope  about  160  feet  northeastward 
and  300  feet  southwestward  to  the  middle  slope.  The  upper  drift 
is  267  feet  below  the  surface  and  43  feet  above  the  middle  gangway, 
and  has  been  driven  each  way  about  300  feet,  connecting  on  the  south- 
west with  the  middle  slope,  as  on  the  lower  level.5 

The  top  of  the  middle  slope  is  at  the  same  elevation  as  the  upper 
one,  and  it  is  about  310  feet  long,  with  two  levels  corresponding  .and 
connecting  with  the  upper  and  middle  levels  on  the  upper  slope.  The 
middle  slope  was  driven  in  rock,  but  the  upper  slope  was  driven  on 
ore  all  the  way,  and  as  the  ore  body  here  is  much  softer  than  in  the 
middle  slope  a great  deal  of  trouble  and  expense  has  been  necessary 
to  keep  the  slope  in  repair.  This  has  led  to  its  proposed  abandonment 
and  to  the  erection  of  permanent  buildings  at  the  middle  slope,  from 
which  all  future  mining  will  probably  be  carried  on.  These  improve- 
ments were  hardly  consummated  when  the  dull  times  of  1880  and 

° D'Invilliers,  E.  V.,  Geology  of  Berks  County:  Second  Geol.  Survey  Pennsylvania,  Kept. 
D3,  1883,  pp.  314-316. 

b This  level  was  afterward  extended  to  a distance  of  about  500  feet  northeast  of  the 
slope  and  reached  beyond  Philadelphia  avenue,  according  to  the  statemnet  of  Richard 
Richards,  former  foreman  of  the  Phoenix  company. 

54370 Bull.  359—08 4 


50 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


1881  led  to  the  closing  of  all  the  mines,  and  the  two  upper  slopes  are 
still  filled  with  water  [1883].  It  is  likewise  proposed  here  to  further 
test  the  property  by  driving  northward  from  the  slope  to  prove  the 
presence  or  absence  of  the  underlying  blue  ore  bed.® 

The  true  foot  wall  in  both  these  slopes  is  an  altered  syenite  carrying 
thin  seams  of  earthy  magnetite  with  dull  luster,  in  many  places 
massed  or  bunched,  and  showing  but  little  crystallization.6  The 
syenite  is  filled  with  pink  feldspar  nodules,  hornblende,  and  epidote, 
all  distinctly  stratified.  In  the  upper  slope,  however,  a dark  green- 
ish-black unctuous  limestone  layer  is  found  at  many  points  between 
the  main  body  of  the  ore  and  the  true  foot  wall,  much  of  it  carrying 
chert  in  large  masses.  The  top  wall  is  a decomposed,  light  greenish- 
gray,  serpentine  limestone,  slaty  and  carrying  crystals  of  pyrite.  The 
ore  rock  is  generally  an  impure  conglomerate  limestone  carrying 
masses  of  dull-colored  crystalline  limestone,  serpentine,  and  magnetic 
ore,  but  the  bulk  of  it  is  a green  to  black  dolomite  with  coatings  of 
calcite.  The  ordinary  run  of  the  mine  shows  a mixture  of  magnetic 
iron  ore,  with  limestone  and  minute  crystals  of  iron  pyrites  diffused 
through  the  mass.  Locally  the  pyrite  occurs  in  large  and  well-de- 
fined crystals. 

Phoenix  lower  slope , or  California  mine.0 — The  developments  here 
consist  [1883]  of  a slope  about  300  feet  long,  from  which  three  levels 
have  been  driven  toward  the  northeast  for  the  purpose  of  working 
the  Hagy  ore  bed,  and  two  toward  the  southwest  to  meet  the  Rhoades 
vein.  The  lowest  level  was  driven  first  for  about  50  feet  through  a 
dark  quartzose  sandy  rock  of  a bluish  color.  The  course  of  the  gang- 
way being  thought  to  be  turned  too  much  toward  the  east  to  strike 
the  ore,  the  next  50  feet  was  driven  more  to  the  north,  likewise  through 
rock,  until  at  a distance  of  110  feet  from  the  foot  of  the  slope  ore  was 
struck.  The  original  northeast  course  was  resumed  and  carried 
through  ore  for  50  feet  more.  The  gangway  at  the  time  of  visit 
showed  a chamber  fully  22  feet  wide,  without  showing  foot  or  hang- 
ing walls.  The  dip  of  this  western  body  of  black  ore  is  probably 
toward  the  southeast  at  a steep  inclination. 

The  middle  drift  is  about  40  feet  vertically  above  the  lowest,  and  in 
driving  northward  from  the  shaft  the  same  characteristics  were  met 
as  already  noted  in  the  lower  level.  The  drift  is  not  parallel  to  the 
lower  level,  but  turns  somewhat  more  toward  the  northeast.  For  the 
first  30  feet  it  passed  through  rock,  beyond  which  the  ore  body  was 
met  in  a rather  pinched  condition. 

The  upper  level  is  driven  northward  from  the  slope  about  176  feet 
ATertically  below  the  surface  of  the  ground.  It  extends  for  about  80 


a Mr.  Richards  states  that  this  exploration  was  made,  hut  that  no  ore  was  found. 
b Compare  with  statement  of  Willis,  p.  41). 
c D'lnvilliers,  E.  V.,  op.  cit.,  pp.  308—311. 


u.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  359  PL.  XIII 


B 


CROSS  SECTION  AT  BOYERTOWN  MINES  (ALONG  LINE  E-F,  PL.  Xh 


BERKS  COUNTY  DEPOSITS. 


51 


feet  along  the  south  line  of  the  old  Eckert  open  cut,  and  the  ore  body 
pinches  toward  the  northeast. 

Exploration  has  been  carried  on  south  of  the  slope,  where  the  work- 
ings consist  of  a rock  tunnel  driven  southwestward  for  about  200 
feet  at  a depth  of  about  176  feet  through  a mixed  micaceous  and 
quartzose  rock  to  the  Rhoades  vein,  which  strikes  about  S.  25°  E. 
and  dips  a little  east  of  north  at  an  angle  of  50°.  A similar  rock 
tunnel  was  driven  from  the  middle  level  in  a nearly  parallel  direc- 
tion, and  from  its  extremity  a raise  has  been  opened  to  strike  the  vein 
on  the  upper  level.  A fine  face  of  ore  30  feet  thick  is  exposed  in  this 
middle  level,  but,  owing  to  its  inferior  quality  as  compared  with  the 
Hagy  ore,  work  has  been  suspended  [1883].  The  thickness  of  this 
bed  varies  greatly,  as  is  the  case  throughout  all  the  mines.  The 
gangue  is  similar  to  that  of  the  Hagy  mine,  being  mostly  silica,  lime, 
and  magnesia,  but  the  ore  is  leaner  in  iron  and  carries  more  sulphur 
and  a little  copper,  being  identical  in  composition  and  physical 
attributes  with  the  blue  ore  of  the  Gabel  mine.  In  the  Gabel  mine 
the  Blue  vein  is  separated  from  the  overlying  Black  vein  by  150  feet, 
more  or  less,®  of  impure  limestone,  but  the  Hagy  and  Rhoades  veins 
are  divided  by  a rock  which  is  apparently  a rotten  quartzose  gneiss, 
though  the  gangue  of  the  ore  itself  in  each  place  is  largely  limestone.6 

Warwick  mine.0 — The  Warwick  mine  has  three  levels  [1883],  with 
numerous  gangways  and  counter  gangways,  many  of  which  have 
been  long  since  abandoned  and  could  not  be  explored.  The  first  level 
is  420  feet  vertically  below  the  surface,  the  second  500  feet,  and  the 
third  567  feet  [corresponding  with  416-foot,  496-foot,  and  555-foot 
levels  as  given  on  PL  X].  Two  gangways  were  driven  on  the  500- 
foot  level,  one  on  the  hanging  wall,  which  is  generally  Mesozoic,  the 
other  extending  toward  the  southeast  and  thence  south  into  the  Gabel 
property  and  showing  generally  a limestonce  foot  wall.  The  average 
horizontal  distance  between  these  gangways  is  about  50  feet,  which 
would  give  a thickness  of  about  25  feet  of  ore,  measured  at  right 
angles  to  the  dip.  The  space  between,  however,  is  by  no  means  en- 
tirely occupied  by  ore,  but  contains  numerous  horses  of  serpentine, 
limestone,  and  greenstone,  as  well  as  many  occurrences  of  pinching 
where  the  foot  and  hanging  walls  come  together.  Pinching  is  par- 
ticularly noteworthy  in  the  north  gangway,  where  about  150  feet 
from  the  shaft  the  ore  is  only  from  3 inches  to  1 foot,  and  again  at 
the  end  of  the  gangway,  where  the  ore  is  entirely  cut  off. 

The  ore  is  found  everywhere  to  lie  in  lenticular-shaped  bodies, 
thinning  out  in  the  line  of  strike  and  swelling  to  immense  bunches  in 

a One  hundred  and  sixty  feet,  as  measured  on  the  map. 

b To  judge  from  the  workings  on  the  176-foot  level  of  the  California  mine,  the  hori- 
zontal distance  between  the  Hagy  vein  and  the  Rhoades  vein  is  about  175  feet,  hut  the 
two  veins  strike  in  very  different  directions — in  fact,  at  an  angle  to  each  other  of  about 
45°.— A.  C.  S. 

c D’Invilliers,  E.  V.,  op.  cit.,  pp.  320-324, 


52 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


the  center,  variously  mixed  with  limestone,  with  which  it  seems  to 
be  here  and  there  intimately  interstratified.  A fine  illustration  of 
this  relation  was  furnished  in  the  lower  [454-foot]  level  of  the  Gabel 
mine,  where  in  a piece  of  limestone  6 inches  thick  there  were  four 
bands  of  interstratified  ore  from  \ to  1 inch  thick. 

From  the  500-foot  level  to  a point  90  feet  out  from  the  shaft  a 
crosscut  was  driven  S.  40°  W.  in  search  of  the  Blue  vein  found  in 
the  Gabel  mine.  It  is  probable  that  this  bed  exists  in  the  extreme 
southwest  corner  of  the  Warwick  tract,  but,  except  at  lower  levels,  it 
w ould  not  pay  to  stope  it,  as  it  must  within  a short  distance  pass  into 
the  adjacent  properties. 

The  crosscut  was  not  driven  far  enough  to  reach  the  Blue  bed,  for 
the  slight  development  of  this  vein  in  the  Gabel  mine  shows  that  it 
has  a decided  tendency  to  bear  toward  the  northwest,  in  the  direction 
of  the  lower  Phoenix  slope.  The  crosscut  was  closed  at  the  time  the 
mine  was  examined,  but  it  was  said  to  have  been  carried  first  through 
10  feet  of  limestone,  then  4 feet  of  ore,  and  for  143  feet  through 
quartzose  sandstone.® 

From  a point  beneath  the  railroad  to  the  boundary  with  the  Gabel 
property  the  south  gangway  on  the  500-foot  level  is  driven  through 
limestone  and  ore,  the  former  being  the  general  foot  wall  and  dipping 
about  35°  SE.  A great  deal  of  ore  has  been  obtained  from  stopings 
carried  up  from  this  gangway  along  the  foot  wall.  Masses  of  calcite, 
bearing  clusters  of  pyrite,  are  seen  in  numerous  places  accompanying 
the  ore. 

Close  to  the  property  line  the  north  edge  of  an  immense  body  of  ore 
appeared,  and  in  parting  the  drift  to  work  it  the  ore  was  found  to 
be  fully  40  feet  thick.  The  absence  of  connected  surveys  led  to  the 
continuation  of  both  drifts  into  the  Gabel  property,  from  which  fully 
8,000  tons  of  ore  was  eventually  extracted.  A magnificent  pillar  of 
excellent  black  ore  still  remains  as  the  support  to  the  roof  of  this  im- 
mense chamber.  A crosscut  from  the  foot  to  the  hanging  wrall  was 
in  ore  for  its  entire  length. 

Inspection  of  the  lowest  567-foot  level  in  this  mine  [555-foot  level 
of  PI.  X]  wfill  show  that  two  gangways  have  been  opened,  connected 
in  two  places  by  crosscuts. 

In  the  twro  parallel  gangways  driven  eastward  from  the  shaft  to 
meet  the  ore  body  a considerable  mass  of  limestone  was  driven 
through,  extending  as  far  as  125  feet  from  the  shaft,  after  which  ore 
was  encountered  to  the  Mesozoic  conglomerate  hanging  wall,  dipping 
here  50°  to  55°  a little  south  of  east.  The  last  60  feet  of  the  southern 
of  these  two  drifts  was  entirely  in  ore,  which  here  spreads  out  to  a 
pinch  within  about  30  feet  to  the  northeast  along  the  main  gangway, 
branching  off  from  the  north  crosscut.  The  quality  of  the  ore  here 


° The  rocks  through  which  this  tunnel  was  run  are  shown  by  Willis  as  diabase. 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  359  PL.  XIV 


a 


BERKS  COUNTY  DEPOSITS. 


53 


was  excellent,  but  it  was  soon  cut  off  by  the  meeting  of  the  limestone 
and  the  Triassic  measures  [conglomerate].  To  the  south-southeast, 
along  the  hanging-wall  gangway,  the  ore  gradually  thins  away,  and 
about  60  feet  below  the  south  crosscut  it  ranges  from  3 inches  to  1 
foot.  This  pinch  corresponds  closely  in  position  and  character  to 
that  already  mentioned  as  occurring  on  the  500-foot  level,  and  the 
gangways  are  essentially  parallel.  The  pinch  on  the  hanging-wall 
gangway  extends  for  50  feet,  to  a point  where  the  gangway  makes 
a decided  turn  toward  the  S.  40°  E. ; here  another  body  of  ore  was 
encountered,  10  feet  thick  and  swelling  into  the  hanging  wall,  but 
pinching  again  in  about  35  feet.  This  ore  was  stoped  up  for  about 
40  feet,  where  it  was  found  to  extend  back  over  the  pinch,  thus  show- 
ing the  presence  of  bulging  and  thinning  on  the  line  of  dip.  The 
S.  40°  E.  course  extends  for  120  feet  to  a point  under  the  railroad, 
where  the  gangway  turns  southward  and  shows  a limestone  top. 
Sixty  feet  beyond,  a greenstone  dike  was  encountered  similar  to  that 
occurring  in  several  places  in  this  and  in  the  500-foot  level  along 
a line  from  this  point  to  the  shaft.  These  dikes  are  nowhere  of  great 
thickness,  and  generally  dip  to  the  northeast.  Where  diabase  is 
present  it  usually  forms  a true  foot  wall,  no  ore  being  found  beyond 
it,  but  in  the  567-foot  level  in  the  hanging-wall  gangway  it  partakes 
more  of  the  character  of  a horse,  having  ore  on  both  sides. 

The  foot-wall  gangway  on  this  level  is  almost  entirely  in  ore,  in 
many  places  with  a very  steep  dip  and  in  one  place  even  overturned. 
Inspection  of  the  mine  map  will  show  that  the  foot-wall  gangway  of 
the  567-foot  level  lies  very  nearly  underneath  the  foot-wall  gangway 
on  the  level  above.  On  both  levels  the  gangways  have  a general 
curve  convex  toward  the  east,  and  toward  the  south  the  dips  become 
lower  and  lower  until  near  the  Gabel  property  line  they  do  not  aver- 
age over  35°  and  here  and  there  fall  to  20°.  Because  of  the  low  dip 
in  the  southern  part  of  the  mine  most  of  the  stoping  has  been  con- 
fined to  the  500-foot  level. 

A little  development  has  been  made  on  the  420-foot  level,  but  here 
the  dip  of  the  vein  carries  the  ore  beyond  the  property  limits  within 
a short  distance,  so  that  no  extensive  work  has  been  done. 

Gabel  mine.a — A vertical  section  through  the  Gabel  No.  1 shaft 
shows — 

Feet. 


Banded  shales,  sandstones,  and  conglomerate,  with  a layer 

of  altered  mud  rock  about  5 feet  thick  at  the  bottom 180 

Black  bedded  ore,  folded  and  broken,  and  consisting  mostly 

of  calcareous  breccia 26 

Limestone 150 

Blue  ore  bed  (measured  across  the  bedding  20  feet) 55 

Chloritic  rock  or  greenstone  [probably  diabase] 74 


D’Invilliers,  E.  V.,  op.  cit.,  pp.  328-330. 


54 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


The  mine  has  two  levels,  the  upper  180  feet  [160?]  and  the  lower 
474  feet  [454].  Some  development  was  carried  on  in  the  upper  level 
close  to  the  shaft,  but  the  ore  was  greatly  mixed  with  a light-green 
limestone  gangue  and  in  addition  was  greatly  broken  and  folded. 
The  underlying  limestone  was  similar  to  that  found  in  the  Warwick 
mine,  being  mostly  a serpentine-green  limestone  of  a light  color,  but 
the  gangue-rock  limestone  is  much  darker  and  in  places  black  from 
the  contained  ore. 

While  mining  in  the  upper  level  the  Gabel  Company  became  con- 
vinced of  the  trespass  that  had  been  made  on  its  property  through 
the  500- foot  level  of  the  Warwick  mine.  From  the  474- foot  level  a 
main  gangway  was  started  toward  the  southeast,  in  which  the  blue 
bed  was  struck  80  feet  from  the  shaft.  This  ore  extended  for  83 
feet,  the  vein  dipping  about  60°.  At  the  Blue  vein  the  course  of  the 
gangway  was  turned  somewhat  to  the  left,  and  the  remaining  part 
of  the  gangway  was  entirely  in  limestone,  at  first  dipping  rather 
steeply  but  afterward  flattening  as  the  Black  vein  was  approached. 
About  175  feet  beyond  the  hanging  wall  of  the  Blue  vein  the  foot 
wall  of  the  Black  vein  was  struck.  The  gangway  came  into  the 
Warwick  Company’s  stopes,  which  had  been  driven  up  from  its  500- 
foot  level  on  a dip  of  about  35°.  In  the  Gabel  shaft  the  two  ore  beds 
and  the  strata  which  lie  between  them  all  dip  about  45°  S.  55°  E. 

The  ore  beds  in  the  Gabel  mine  are  like  those  in  the  other  shafts. 
They  occur  in  masses  a,nd  bunches  40  feet  thick,  which  pinch  out  to 
mere  leaders  and  are  therefore  by  no  means  continuous  bodies  of  ore. 
The  ores,  however,  show  one  difference,  in  that  they  are  harder  and 
more  compact  than  in  the  other  mines,  probably  on  account  of  their 
proximity  to  the  Gabel  Hill  dike,  which  may  have  exerted  some  in- 
fluence in  altering  their  physical  properties. 

From  the  474-foot  level  two  gangways  have  been  driven  in  the 
foot  wall  of  the  Black  ore  bed.  Owing  to  its  great  thickness  here  and 
large  limestone  partings,  stoping  has  been  carried  up  almost  to  the 
shaft,  where  the  Black  vein  was  cut  180  feet  below  the  surface,  thus 
proving  the  identity  of  the  brecciated  bed  there  found  with  the  mag- 
nificent body  of  ore  in  the  lower  part  of  the  mine. 

The  Warwick  gangways  have  likewise  been  extended  along  the 
hanging  wall  [“new  red” — that  is,  limestone  conglomerate],  but 
not  from  the  500-foot  level,  being  started  from  the  stopings  above. 
These  drifts  along  the  hanging  wall,  as  well  as  those  on  the  foot  wall, 
have  been  carried  a considerable  distance  to  the  south,  two  of  them 
being  at  least  as  far  out  as  the  barn.  These  gangways  exhibit  the 
tendency  of  the  ore  body  to  swing  around  Gabel  Hill. 

Some  stoping  has  been  done  on  the  Blue  ore  bed,  but  the  inferior 
quality  of  this  ore  delays  its  extended  development.  The  company 
intends  [1883]  to  sink  another  lift  in  the  near  future,  from  which 


U.  S.  GEOLOGICAL  SURVEY 


K 


100 


-L 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  NO.  359  PL.  XV 


CROSS  SECTION  AT  BOYERTOWN  MINES  (ALONG  LINE  K-L,  PL.  X). 


BERKS  COUNTY  DEPOSITS. 


55 


it  will  drive  to  the  southeast,  thus  opening  a third  level  on  this 
valuable  ore  tract.  [See  552-foot  level,  PI.  X.] 

A crosscut  was  driven  from  the  474-foot  level  toward  the  south- 
west into  the  hill,  but  the  ore  was  found  to  be  cut  off  in  this  direction 
by  the  diorite  dike  which  outcrops  on  the  north  side  of  Gabel  Hill. 

LATER  DEVELOPMENTS. 

The  descriptions  which  have  been  given  include  the  tunnels  and 
shafts  opened  before  1883.  Between  that  year  and  1893  the  workings 
of  the  various  mines  were  considerably  extended.  Gabel  shaft  Xo.  1 
was  carried  to  a depth  of  about  570  feet,  and  on  the  552-foot  level  a 
crosscut  was  run  to  the  Blue  and  Black  veins,  giving  stoping  ground 
of  98  feet  vertically  below  the  next  level  above.  Gabel  shaft  Xo.  2 
was  sunk  to  a depth  of  665  feet.  The  shaft  encountered  the  Black 
vein  at  about  640  feet,  but  the  thickness  of  the  ore  body  can  not  be 
stated.  The  workings  from  the  shaft  comprise  two  short  drifts  in 
the  ore  body.  The  northerly  drift,  about  55  feet  long,  is  connected 
by  a raise  with  the  552-level  of  Gabel  Xo.  1 mine.  The  southerly 
drift  is  25  feet  long  and  from  its  end  a crosscut  tunnel  penetrates  the 
foot  wall.  The  length  of  this  tunnel  is  about  360  feet.  About  35 
feet  from  its  end  short  drifts,  which  extend  to  the  right  and  left,  are 
supposed  to  follow  the  hanging  wall  of  the  Blue  vein.  Unfor- 
tunately no  person  was  found  who  had  worked  in  this  tunnel,  and  its 
depth  below  the  surface  is  not  accurately  known.  Between  shaft  Xo. 
1 (where  the  ore  was  first  cut  at  a depth  of  about  180  feet)  and  shaft 
Xo.  2 the  Black  vein  had  been  proved  as  a continuous  layer  for  about 
800  feet  in  the  direction  of  dip.  On  the  trespass  level  the  drifts  in 
ore  within  the  Gabel  property  were  about  250  feet  long,  and  from  the 
Warwick  shaft  the  vein  had  been  followed  for  400  feet  before  cross- 
ing the  property  line. 

The  Blue  vein  lies  below  the  Black  vein  somewhat  more  than  100 
feet,  measured  normal  to  the  bedding,  or  from  160  feet  to  325  feet 
measured  along  the  various  crosscuts.  It  has  been  mined  on  the 
dip  to  the  height  of  about  375  feet  and  on  the  strike  to  a maximum 
length  of  about  250  feet.  On  the  640-foot  level  neither  vein  had 
been  fully  developed  when  mining  was  suspended.  To  judge  from 
the  course  of  the  Blue  vein  in  the  higher  workings,  it  is  not  likely  to 
extend  more  than  a short  distance  into  the  Warwick  plot.  All  of 
shaft  Xo.  1 below  the  Blue  vein — that  is,  below  a level  about  400 
feet  from  the  top — is  supposed  to  be  in  diabase  (greenstone  of  D’ln- 
villiers’s  description) , though  no  positive  statement  to  this  effect  was 
made  either  by  Willis  or  by  D’lnvilliers. 

Xo  information  has  been  procured  in  regard  to  the  behavior  of 
the  ore  bodies  in  the  southernmost  workings  of  Gabel  Xo.  1 mine,  but 
the  fact  that  none  of  the  drifts  were  extended  for  more  than  200  feet 


56 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


from  the  crosscut  may  indicate  that  both  veins  come  to  an  edge  in 
this  ground.  In  view  of  the  uncertainty  which  exists  on  this  point 
it  would  be  safer  to  lay  out  any  exploration  for  the  veins  at  lower 
levels  southeast  of  the  shaft  rather  than  south  or  southwest. 

In  the  Warwick  mine  two  lifts  were  sunk  after  1883.  On  the  610- 
foot  level  the  vein  was  found  to  be  double  (as  on  the  555-foot  level), 
and  both  the  foot-wall  and  hanging-wall  leads  were  developed  by 
drifts  extending  southward  nearly  to  the  property  line. 

An  extension  of  about  120  feet  would  connect  the  foot-wall  gang- 
way with  the  640-foot  level  of  the  Gabel  mine.  On  the  610-foot  level 
a crosscut  200  feet  long  which  was  run  into  the  foot  wall  nearly  to 
the  property  line  failed  to  locate  the  Blue  vein,  but  nothing  is  known 
concerning  the  rocks  penetrated.  Unless  diabase  was  encountered 
it  would  seem  to  be  worth  while,  in  view  of  the  present  control  of 
both  the  Gabel  and  Warwick  tracts  by  the  same  company,  to  con- 
tinue this  tunnel  to  the  diabase,  for  in  the  Gabel  mine,  at  about  the 
same  elevation,  the  horizontal  distance  between  the  Black  and  Blue 
veins  was  about  325  feet.  In  the  eastern  drifts  of  Gabel  No.  1 mine 
the  manner  in  which  the  Blue  vein  curves  toward  the  north  and  the 
fact  that  the  drift  on  the  552-foot  level  if  continued  in  its  course 
would  pass  nearly  under  the  end  of  the  drift  on  the  454-foot  level 
suggest  that  in  this  ground  the  Blue  vein  stands  very  steeply. 

In  a search  for  the  Hagy  vein  two  tunnels  were  run  into  the  hang- 
ing wall  on  the  610-foot  level  about  100  feet  east  of  the  shaft. 
Though  the  vein  was  not  located,  it  is  probable  that  it  may  yet  be 
discovered  by  extending  the  exploration  toward  the  north  or  north- 
west. This  point  is  referred  to  again  on  page  59. 

The  workings  on  the  Warwick  683-foot  level,  so  far  as  is  shown 
on  the  map  (PI.  X),  comprise  a gangway  200  feet  long,  apparently 
on  the  foot  wall  of  the  vein,  and  two  crosscuts,  one  into  the  foot 
wall  and  the  other  started  toward  the  hanging  wTall.  No  data  have 
been  procured  concerning  the  ore  body  on  this  level,  and  the  nature 
of  the  rock  encountered  in  the  lower  part  of  the  shaft  is  not  known. 
It  may  be  suggested  that  if  the  Warwick  shaft  penetrated  any  con- 
siderable mass  of  diabase  there  can  be  no  further  probability  of 
encountering  either  the  Blue  vein  or  the  Rhoades  vein  on  the  lowest 
level,  as  the  foot  wall  of  both  is  the  Gabel  Hill  intrusive  mass.  On 
the  other  hand,  if  the  main  mass  of  diabase  has  not  been  encountered 
there  is  still  a chance  of  finding  ore  by  locating  and  exploring  the 
diabase  contact. 

In  the  California  mine  the  workings  now  reach  a vertical  depth 
of  390  feet,  two  levels  having  been  opened  below  the  200-foot  level, 
which  was  the  lowest  in  1883.  Just  beneath  the  old  sump  a body 
of  ore  was  encountered  which  was  known  as  ore  No.  2.  On  the  305- 
foot  level,  where  the  same  bed  was  struck  about  20  feet  from  the 


GEOLOGICAL  SURVEY  BULLETIN  NO.  359 


PLAN  OF  CALIFORNIA  AND  WARWICK  MINES  AT  BOYERTOWN,  PA.,  SHOWING  POSITION  OF  FAULT. 


BERKS  COUNTY  DEPOSITS. 


57 


slope,  it  extends  for  about  30  feet  along  the  drift  and  is  reported  to 
be  18  to  20  feet  thick.  On  this  level  about  45  feet  beyond  ore  Xo. 
2,  or  95  feet  distant  from  the  slope,  the  Hagv  vein  was  encountered. 
Along  the  hanging  wall  it  was  mined  for  125  feet.  On  the  390-foot 
level  ore  Xo.  2 was  cut  about  75  feet  from  the  slope  and  it  con- 
tinued in  the  drift  for  about  30  feet,  with  a maximum  thickness  of 
-bout  20  feet.  Fifty  feet  farther  on  the  Hagy  vein  appears  and, 
jeing  cut  diagonally,  continues  for  about  90  feet  in  the  drift.  This 
vein  has  been  stoped  from  the  390-foot  level  to  the  bottom  of  the 
Hagy  pit,  or  about  500  feet  along  the  dip. 

In  the  California  mine  the  southernmost  workings  in  the  390-foot 
level  on  ore  Xo.  2 are  about  60  feet  distant  from  the  Warwick 
shaft  and  about  30  feet  higher  than  the  416- foot  level  of  the  latter 
mine  on  which  the  Warwick  vein  was  first  opened.  The  proximity 
•f  these  workings  leaves  little  doubt  that  ore  Xo.  2 and  the  War- 
wick  vein  are  parts  of  the  same  ore  body,  as  has  been  commonly 
supposed  by  persons  most  familiar  with  these  mines. 

PRACTICAL  CONCLUSIONS. 

Facts  are  not  at  hand  to  warrant  an  unreserved  statement  of  the 
relation  existing  between  ore  Xo.  2 and  the  Hagy  body ; at  the  same 
time,  it  is  thought  that  they  are  probably  parts  of  a single  vein  which 
has  been  separated  b}^  faulting.  The  existence  of  a fault  is  surmised 
from  the  knowledge  that  in  the  Warwick  mine  limestone  conglom- 
erate forms  the  hanging  wall  of  the  vein  at  least  as  deep  as  the  555- 
foot  level,  whereas  in  the  upper  levels  of  the  California  mine  the 
same  rock  lies  above  the  Hagy  vein.  If,  then,  the  Warwick  vein 
holds  its  position  just  beneath  the  conglomerate  as  it  extends  upward 
into  the  California  mine,  and  if  the  Hagy  vein  holds  its  position 
beneath  the  conglomerate  as  it  extends  downward  from  the  200- foot 
level  to  the  390-foot  level  there  can  be  no  doubt  that  both  the  ore 
layer  and  the  overlying  conglomerate  have  been  offset  along  a fault 
break.  The  same  conclusion  would  follow  if  it  were  found  that  con- 
glomerate forms  the  hanging  wall  both  of  ore  Xo.  2 and  of  the  Hagy 
vein  on  the  390-foot  level  of  the  California  mine.  The  horizontal 
displacement  along  the  fault  appears  to  be  about  125  feet  (Pis.  VIII 
and  XVI). 

On  the  assumption  that  there  is  a fault  and  that  the  Hagy  vein  con- 
tinues to  dip  about  65°,  as  noted  on  the  map  (PI.  X)  at  the  end  of 
the  390-foot  level,  California  mine,  the  positions  of  the  foot  wall  on 
the  555-foot,  610-foot,  and  683-foot  levels  will  be  approximately 
as  shown  by  PL  XVI. 

On  the  390-foot  level  in  the  California  mine,  according  to  Mr. 
Richards,  exploration  was  carried  in  lean  ore  for  50  or  60  feet  toward 


58 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


the  north  along  the  strike  of  the  vein.  This  makes  it  appear  that 
mineralization  dies  out  in  this  direction.  A similar  decrease  in 
values  having  been  found  in  a 100- foot  westerly  drift  from  the 
middle  slope,  the  intervening  ground  has  been  judged  to  be  barren. 
Whether  it  is  really  so  or  not  of  course  can  not  be  decided  without 
actual  exploration,  but  the  existence  of  a fault  break  or  of  several 
breaks  between  the  workings  of  the  California  mine  and  those  of  the 
Phoenix  mine  on  the  East  vein  is  strongly  suggested  by  the  rela- 
tive positions  and  different  strikes  of  the  Hagy  and  East  veins. 
A good  idea  of  these  features  may  be  obtained  from  the  plan  giving 
the  projected  positions  of  the  several  veins  on  a level  surface  400  feet 
below  the  top  of  Gabel  No.  1 shaft  (PI.  VIII).  Mr.  Eichards  states 
that  on  the  lowest  level  of  the  workings  on  the  East  vein  good 
ore  continued  east  of  the  upper  slope  about  100  feet,  beyond  which 
lean  ore  was  penetrated  for  perhaps  50  feet.  On  the  middle  level, 
43  feet  vertically  above,  mining  was  continued  toward  the  east  for 
150  feet,  and  on  the  upper  level,  43  feet  higher,  good  ore  was  found 
for  fully  500  feet.  The  total  length  of  the  ore  body  on  the  upper 
level  was  about  750  feet.  Corresponding  roughly  with  the  bottom 
of  the  minable  ore,  which  is  found  farther  and  farther  west  as  depth 
is  gained,  the  upper  edge  lies  more  than  100  feet  east  of  the  middle 
slope  on  the  upper  level,  about  25  feet  east  on  the  middle  level,  and 
some  distance  west  of  the  slope  at  the  bottom  of  the  mine.  It  is  thus 
apparent  that,  in  addition  to  its  southeastern  dip,  the  ore  shoot 
pitches  toward  the  south,  and  also  that  if  this  pitch  continues  the 
ore  body  must  pass  into  the  block  of  ground  bounded  by  Third  street, 
the  mineral-reserve  line,  and  the  railroad.  How  far  it  may  persist 
in  this  direction  can  not  be  suggested.  It  may  or  may  not  extend  as 
far  as  the  ore  horizon  remains  unbroken. 

It  is  strongly  suspected,  as  already  stated,  that  at  least  one  displace- 
ment of  the  ore  horizon — that  is  to  say,  the  surface  between  the  limy 
strata  and  the  limestone  conglomerate — exists  between  the  middle 
slope  and  the  workings  of  the  Hagy  vein  of  the  California  mine. 
Three  faults  with  horizontal  displacements  equal  to  that  of  the  fault 
supposed  to  exist  between  the  Warwick  and  Hagy  ore  bodies  would 
suffice  to  throw  the  ore  horizon  from  the  place  it  occupies  in  the  Cal- 
ifornia mine  into  the  observed  position  of  the  East  vein.  (See  fig.  7.) 
If  the  Hagy  vein  is  ever  found  in  the  lower  workings  of  the  War- 
wick mine,  further  prospecting  in  the  direction  of  the  estimated 
downward  extension  of  the  East  vein  would  seem  warranted.  The 
intervening  block  of  ground  may  not  contain  Avorkable  ore  near  the 
surface,  but  is  perhaps  more  likely  to  carry  ore  bodies  as  depth  is 
gained,  because  the  mineralizing  waters  which  produced  the  ore  are 
believed  to  have  come  from  below. 


BERKS  COUNTY  DEPOSITS. 


59 


The  chances  of  finding  the  Hagy  and  East  veins  above  the  lowest 
level  of  the  Warwick  mine  are  thought  to  fully  warrant  explorations 
along  the  lines  of  the  foregoing  suggestions,  but  the  ground  that  offers 
the  strongest  inducement  for  exploration  is  that  which  lies  beyond 
the  Warwick  and  Gabel  workings  in  the  direction  of  the  dip  of  the 
Warwick  ore  body.  No  extended  argument  is  needed  to  show  the 
advisability  of  testing  the  further  persistence  of  an  ore  body  like  the 
Warwick  or  Black  vein,  which  has  been  followed  along  its  course 
almost  continuously  (though  swelling  and  pinching)  for  1,000  feet 
and  along  its  dip  for  800  feet,  with  no  signs  of  failure  in  the  lowest 
levels  that  have  been  opened.  The  map  and  cross  sections  (Pis. 
X-XV)  which  accompany  this  report  afford  adequate  data  for  laying 


Fig.  7. — Ideal  sketch  showing  possible  type  of  structure  in  ground  between  Hagy  vein 
and  East  vein.  Datum  of  plan,  400  feet  below  top  of  Gabel  No.  1 shaft. 


out  an  advantageous  plan  of  prospecting  the  veins  by  means  of  the 
diamond  drill. 

The  theory  which  has  been  developed  concerning  the  origin  of  the 
Boyertown  ore  bodies  is  based  on  the  analogies  between  these  deposits 
and  those  of  similar  character  at  other  places  in  the  State,  each  of 
which  exhibits  a close  dependence  on  adjacent  bodies  of  intrusive 
diabase.  It  is  noteworthy  that  all  the  ore  bodies  except  the  East 
vein  lie  just  beyond  the  termination  of  the  diabase  sill  which  occurs 
along  the  northwest  side  of  Gabel  Hill.  Apparently  underground 
the  sill  dips  with  the  bedding  of  the  invaded  rock  and  the  edge 
which  it  presents  toward  the  north  pitches  steeply  in  such  a direction 
that  it  passes  beneath  the  Warwick  and  Gabel  workings.  The  Blue 
vein  in  the  Gabel  mine  appears  to  follow  the  upper  surface  of  the 
sill,  but  the  Rhoades  vein  seems  to  lie  against  its  blunt  edge.  In  the 


60 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Gabel  mine  more  than  100  feet  of  limy  strata  lie  between  the  diabase 
and  the  conglomerate  which  caps  the  Black  vein,  but  all  indications 
on  the  surface  favor  the  conclusion  that  the  conglomerate  extends 
northward  almost  if  not  actually  to  the  walls  of  the  diabase.  As  in 
the  mine  it  appears  that  the  diabase  follows  the  stratification  of  the 
limy  beds,  the  near  approach  or  actual  contact  of  the  conglomerate 
and  the  diabase  at  the  surface  signifies  one  of  two  things — either  that 
the  intrusive  mass  cuts  across  the  stratification  above  the  point  where 
the  contact  is  penetrated  by  Gabel  No.  1 shaft,  or  that  the  parallelism 
between  the  stratification  of  the  Paleozoic  and  Mesozoic  rocks,  which 
apparently  exists  elsewhere  in  the  mine,  does  not  hold  in  this  place. 
A plausible  suggestion  of  what  the  relations  may  be  in  depth  is 


Fig.  8. — Sketch  section  illustrating  possible  relation  of  Black  vein  to  buried  edge 
of  a diabase  sill  at  Gabel  mines. 


illustrated  in  fig.  8.  The  presence  of  several  sills  south  of  Boyer- 
town,  as  shown  on  the  sketch  map,  the  manner  in  which  these  sills 
terminate,  and  the  probable  existence  of  an  underlay  of  diabase 
beneath  the  structural  basin  which  has  been  described  all  suggest 
the  validity  of  the  assumption  that  one  or  more  buried  sills  exist 
in  the  region  southeast  and  east  of  the  Boyertown  mines. 

The  emergence  of  a minor  intrusion  of  diabase  near  West  Swamp 
Creek,  1 mile  northeast  of  New  Berlinville,  and  of  a great  mass  east 
of  Bechtelsville  suggest  that  the  edges  of  the  sills  representing  the 
upward  limit  of  intrusion  on  the  northwest  side  of  the  synclinal  basin 
probably  lie  at  no  great  depth  and  not  very  far  back  (southeast)  of 
the  boundary  between  the  Mesozoic  area  and  that  occupied  by  the 


BERKS  COUNTY  DEPOSITS. 


61 


older  formations.  If  the  presence  of  the  buried  sills  in  this  vicinity 
were  known  to  be  a fact,  and  if  the  place  could  be  determined  where 
any  one  of  them  penetrates  strata  corresponding  to  those  in  which 
the  Boyertown  deposits  occur,  the  existence  of  a series  of  iron-ore 
deposits  in  the  limy  strata  near  the  diabase  might  be  suggested. 
The  absence  of  knowledge  on  these  two  points  leaves  the  whole 
question  in  the  light  of  a speculation,  with  the  hazards  rather  too 
great  to  justify  recommending  the  expenditure  which  would  be  re- 
quired to  make  a practical  test.  The  imaginary  position  of  the 


Mesozoic  red  sandstones  • Diabase 

and  shales 


Fig.  9. — Geologic  sketch  map  of  vicinity  of  Boyertown,  showing 
imaginary  position  of  edge  of  buried  sill. 

upper  edge  of  the  supposed  sill  is  shown  in  plan  on  the  sketch  map, 

fig.  9. 

DEPOSITS  SOUTHWEST  OF  BOYERTOWN. 

South  of  the  Boyertown  mines  the  northwest  slope  of  Gabel  Hill 
is  formed  by  diabase,  the  hill  itself  and  the  connecting  ridge  for  a 
mile  or  more,  toward  the  south  being  formed  by  baked  and  indurated 
shales  and  sandstones.  At  the  surface  this  mass  of  diabase  ends  as 
an  apparently  blunt  wedge  south  of  the  ground  in  which  the  ore 
deposits  have  been  found,  and  as  nearly  as  can  be  determined  it  comes 
to  the  surface  just  at  the  base  of  the  Mesozoic  beds  where  they  over- 
lap on  the  ore-bearing  strata.  In  this  position  the  diabase,  having  the 
form  of  a sill,  extends  for  three-fourths  of  a mile  southwestward  and 


62 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


then,  turning  down  the  valley  of  Ironstone  Creek,  cuts  back  into  the 
Mesozoic  area.  The  western  edge  of  this  sill  has  not  been  seen  at  any 
place  because  it  comes  to  the  surface  beneath  a mantle  of  loose  debris, 
but  its  eastern  contact  was  encountered  at  the  old  Brower  iron  mine 
on  the  hill  slope  opposite  the  upper  end  of  Wren’s  ice  pond,  about 
half  a mile  southwest  of  the  Rhoades  mine.  The  Brower  ore  at  this 
place  was  discovered  in  a post  hole. 

Richard  Richards,  of  Boyertown,  who  had  charge  of  this  property 
in  1857  and  1858,  states  that  he  extracted  more  than  2,000  tons  of  mag- 
netite ore  from  an  irregular  layer  having  a northeast-southwest  strike, 
a dip  of  35°  or  40°  SE.,  and  a maximum  thickness  of  about  8 feet. 
The  mine  was  worked  by  means  of  a tunnel  and  two  shafts,  and  ore 
was  stoped  from  two  levels  to  a depth  of  about  70  feet  and  to  a length 
on  the  strike  of  about  50  feet.  Examination  of  the  locality  shows  that 
the  ore  layer  occurred  very  near  if  not  exactly  in  contact  with  the 
upper  side  of  the  diabase  sill,  under  a hanging  wall  of  flinty  baked 
shale  or  sandstone.  Taken  by  itself  the  occurrence  of  ore  at  this  place 
is  an  all  but  evident  instance  of  ore  segregation  during  igneous  or  so- 
called  contact  metamorphism,  and  considered  in  the  light  of  the  many 
like  deposits  closely  associated  with  intrusive  diabase  at  other  places 
it  must  be  accepted  as  a deposit  of  this  variety. 

About  300  yards  southwest  of  the  Brower  mine,  back  of  the  J.  Wren 
house,  a short  tunnel  with  its  mouth  in  diabase  was  started  toward  the 
contact,  but  no  information  has  been  obtained  concerning  what  was 
found  at  this  place,  nor  concerning  a shaft  lying  between  the  Wren 
tunnel  and  the  Brower  mine,  shown  on  the  topographic  map  of  the 
Second  Geological  Survey  of  Pennsylvania. 

About  one-fourth  mile  southwest  of  the  Rhoades  mine,  on  the  hill 
slope  about  50  feet  above  the  level  of  the  railroad  track,  a shaft 
(known  as  the  Rhoades  and  Grim  shaft)  has  been  sunk  to  a depth  of 
40  or  50  feet,  to  judge  from  the  material  on  the  dump.  Nothing  but 
diabase  seems  to  have  been  encountered  at  this  place.  East  and  some- 
what north  of  this  shaft  a tunnel  of  unknown  length  was  run  into 
Gabel  Hill,  but  no  person  was  found  having  any  knowledge  of  this 
work.  The  mouth  of  the  tunnel  is  situated  very  near  the  eastern  or 
upper  edge  of  the  diabase  sill,  and  it  seems  that  Mesozoic  strata  must 
have  been  penetrated. 

It  is  not  at  all  unlikely  that  other  masses  of  ore  like  those  of  the 
Brower  mine  exist  along  the  east  contact  of  the  sill,  but  as  no  limy 
strata  are  known  to  occur  on  the  upper  side  of  the  diabase,  this  ground 
is  not  regarded  as  offering  much  inducement  for  prospecting.  West 
of  the  diabase,  conditions  are  probably  more  favorable,  on  the  sup- 
position that  the  strata  which  carry  the  Boyertown  veins  are  here  in 
contact  with  the  under  side  of  the  sill,  but  the  valley  of  Ironstone 
Creek  is  not  a favorable  place  for  making  excavations,  and  it  seems 


BERKS  COUNTY  DEPOSITS. 


63 


that  any  exploration  of  the  under  side  of  the  diabase  should  be  under- 
taken by  means  of  the  diamond  drill. 

DEPOSITS  NORTH  OF  BOYERTOWN. 

About  2 miles  north  by  northeast  of  Boyertown  there  has  been  some 
exploration  for  iron  ore  on  the  south  side  of  the  group  of  diabase 
hills  southeast  of  Bechtelsville.  The  position  of  two  shafts  is  shown 
on  the  topographic  map  of  Berks  County,  issued  by  the  Second  Geo- 
logical Survey  of  Pennsylvania,  though  no  essential  data  are  given 
in  the  Berks  County  report  beyond  the  statement  that  some  excellent 


Mesozoic  red  sandstones  Diabase  Old  mines  and  prospects 

and  shales 


Fig.  10. — Geologic  sketch  map  of  region  northeast  of  Boyertown. 

ore  was  taken  from  an  opening  known  as  the  Gilbert  shaft.  The 
shafts  mentioned  were  not  found  during  the  present  investigation, 
but  from  their  indicated  position  they  are  situated  within  Mesozoic 
strata,  which  come  up  onto  the  diabase  rock  from  the  south. 

The  diabase  covers  a roughly  triangular  area  of  nearly  2 square 
miles,  which  lies  between  West  Swamp  Creek  and  a tributary  known 
as  Middle  Creek.  From  the  southeast  corner  of  this  area  an  arm  ex- 
tends for  about  1J  miles  toward  the  southeast.  The  mass  of  diabase 
is  nearly  surrounded  by  Mesozoic  strata,  which  appear  to  lap  onto  it 
from  the  east  and  from  the  south.  (See  fig.  10.)  On  the  northwest 


64 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


the  structural  relations  are  obscure,  but  from  the  rock  fragments 
scattered  over  the  fields  the  Mesozoic  rocks  are  known  to  be  present 
along  the  base  of  the  hill  above  the  wagon  road  to  a point  within 
one- fourth  mile  of  the  bridge  across  West  Swamp  Creek.  Near  the 
turn  in  the  road,  a short  distance  northeast  of  this  bridge,  blue  Paleo- 
zoic limestones  are  exposed,  and  above  them  baked  shales,  which  may 
belong  to  the  Mesozoic.  This  shale  seems  to  dip  toward  the  hill  at  a 
low  angle,  as  if  it  would  pass  beneath  the  mass  of  diabase  which 
outcrops  a short  distance  up  the  slope.  The  blue  limestone  is  not 
metamorphosed  to  any  marked  degree. 

On  every  side  of  the  diabase  the  Mesozoic  rocks,  including  shale, 
sandstone,  and  limestone  conglomerate,  have  been  considerably  baked, 
and  this  induration  extends  in  places  as  far  as  one-half  mile  from  the 
contact.  Loose  fragments  of  limestone  conglomerate  containing 
abundant  spangles  of  hematite  may  be  found  at  several  places  along 
the  ridge  east  of  Middle  Creek,  and  similar  material  is  abundant  on 
the  hill  slope  about  1 mile  southeast  of  Eshbach.  On  the  south  side 
of  the  diabase  hills  both  specular  hematite  and  magnetite  were  noted 
in  material  revealed  in  a cutting  along  the  east-west  road  a few 
hundred  yards  west  of  the  crossroads  1J  miles  northeast  of  New 
Berlinville.  This  locality  is  near  one  of  the  old  prospecting  shafts 
mentioned  above. 

Although  the  presence  of  hematite  in  the  baked  rocks  which  sur- 
round the  diabase  shows  that  certain  conditions  favorable  for  the 
formation  of  ore  existed,  it  does  not  seem  that  any  large  bodies  of  ore 
are  likely  to  be  encountered  in  the  Mesozoic  strata.  The  exposures 
are  not  sufficient  to  indicate  how  much  limestone  conglomerate  exists 
in  the  neighborhood,  but  it  is  probably  not  present  in  any  such 
amount  as  at  Dillsburg,  York  County,  where  magnetite  ore  deposits 
are  associated  with  beds  of  this  rock  in  the  vicinity  of  diabase 
intrusions. 

Near  the  diabase  there  is  only  one  exposure  of  the  Paleozoic  lime- 
stone which  is  known  to  occupy  the  valley  lying  west  of  the  diabase 
hills,  so  that  almost  nothing  is  known  of  the  structural  relations  of 
this  rock  to  the  Mesozoic  strata  and  to  the  diabase.  It  is  probable, 
however,  that  the  limestones  are  here  overlapped  by  the  Mesozoic 
strata  in  much  the  same  way  as  in  the  vicinity  of  the  Boyertown 
mines,  and  if  this  is  so  there  is  a possibility  tl^at  the  ore  bodies  may 
exist  in  depth  beneath  the  Mesozoic  rocks  which  occur  west  of  the 
diabase  mass.  Though  this  point  could  be  readily  tested  by  a series 
of  drill  holes  along  the  western  portion  of  the  diabase  area,  such  ex- 
ploration would  be  regarded  as  a hazardous  project  from  a practical 
standpoint. 

Iron  ore  is  said  to  have  been  extracted  from  workings  known  as 
the  Fegley  mine,  situated  well  within  the  diabase  area  on  the  north 


BERKS  COUNTY  DEPOSITS. 


65 


side  of  the  little  brook  about  one-fourth  mile  north  of  the  Gilbert 
shaft.  A suggestion  concerning  the  manner  in  which  the  ore  occurs 
in  this  place  was  obtained  from  material  on  the  dump  at  the  tunnel 
mouth.  A large  fragment  of  diabase  was  found,  on  one  side  of  which 
there  was  a coating  of  ore  1 inch  thick  composed  of  crystalline  mag- 
netite intergrown  with  a minor  amount  of  feldspar.  Appearances 
indicate  that  the  magnetite  was  segregated  in  a crevice  traversing 
the  diabase.  There  is  no  sharp  division  between  the  rock  and  the 
ore,  a fact  which  suggests  that  the  magnetite  and  accompanying 
feldspar  may  have  been  deposited  by  vaporous  solutions  derived  from 
the  deeper-seated  part  of  the  diabase  mass  shortly  after  the  period  of 
intrusion. 

In  many  places  the  diabase  intrusions  in  the  Mesozoic  area  contain 
very  considerable  amounts  of  magnetite  as  a mineral  constituent, 
but  this  is  the  only  place  that  has  come  to  the  writer’s  attention  where 
magnetite  has  been  found  segregated  in  a definite  vein  inclosed  by 
the  igneous  rock.  This  occurrence  has  a bearing  on  the  general  prob- 
lem of  the  genesis  of  deposits  of  the  Cornwall  type,  affording  good 
evidence  that  the  diabase  rock  could  have  been  the  actual  source  of 
the  ore- forming  solutions  as  well  as  of  the  energy  which  caused  the 
circulation  of  the  mineralizing  waters.  Elsewhere,  though  the  influ- 
ence of  the  diabase  intrusions  is  everywhere  noteworthy,  it  has  not 
been  possible  to  show  definitely  that  the  solutions  have  emanated 
from  the  intrusive  rock. 

A shallow  pit  has  been  sunk  in  search  of  copper  ore  in  a road-metal 
quarry  beside  the  wagon  road  half  a mile  west  of  Congo  post-office, 
near  the  end  of  the  arm  of  diabase  which  extends  toward  the  south- 
west from  the  main  triangular  area.  In  the  walls  of  this  pit  may  be 
seen  a veinlet  about  an  inch  wide,  composed  mainly  of  hornblende  and 
feldspar  containing  scattered  bunches  of  chalcopyrite.  The  horn- 
blende of  the  vein  appears  to  have  grown  out  from  the  walls  of  a 
crevice,  and  the  material  of  the  vein  is  thus  closely  knit  to  that  of  the 
inclosing  rock,  as  in  the  magnetite  vein  described  above.  It  is  sug- 
gested that  this  veinlet  was  formed  in  a manner  similar  to  that  sug- 
gested for  the  magnetite  vein.  In  a recent  paper  on  the  copper 
deposits  of  New  Jersey  by  J.  Y.  Lewis®  the  source  of  this  metal  is 
believed  to  have  been  the  diabase  intrusions  which  in  each  place  are 
associated  with  the  ore  occurrence. 

JONES  MINE. 

The  Jones  mine,  also  known  as  the  Warwick  ^mine  because  it  was 
formerly  worked  by  the  Warwick  Iron  Company,  is  situated  about 
three-fourths  of  a mile  east  of  Joanna  station  and  1J  miles  northwest 

a Copper  deposits  of  the  New  Jersey  Triassic : Econ.  Geology,  vol.  2,  1907,  pp.  242-257. 

54370— Bull.  359—08 5 


66 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


of  Elverson,  on  the  Wilmington  division  of  the  Philadelphia  and 
Reading  Railroad.  (See  PI.  XVII.)  This  mine  is  in  Berks  County, 
about  4 miles  west-northwest  of  the  Warwick  mines  in  Chester 
County.  Part  of  the  description  of  the  Jones  mine  by  H.  D.  Rogers 
is  here  given : ° 

Tlie  chief  mine  is  an  open  excavation  covering  rather  more  than  5 acres,  and 
there  is  another  to  the  south  of  it  covering  about  1 acre  [Kinney  mine].  Mag- 
nesian limestone  bounds  the  ore  on  the  northern  edge  of  the  principal  excava- 
tion. Here  there  is  a mine  shaft  180  feet  deep  * * *.  The  shaft  enters  the 

limestone  at  a depth  of  50  feet,  and  a boring  20  feet  from  the  bottom  of  the 
shaft  is  still  in  this  rock. 

A dike  of  trap  rock  cuts  the  ore-bearing  strata  near  the  southern  side  of  the 
pit  and  produces  phenomena  precisely  identical  with  those  caused  by  the  trap 
dikes  in  the  Cornwall-Lebanon  mines,  converting  the  ore  to  a more  highly 
crystalline  form  and  endowing  it  partially  with  magnetism.  As  in  every  such 
instance,  the  ore  is  richest  and  purest  adjacent  to.  the  trap  rock.  This  is 
equally  the  case  in  the  southern  or  smaller  mine.  The  strata  dip  N.  30°  W. 
at  about  20° ; and  in  the  northern  bank  of  the  large  mine  we  may  perceive  the 
Auroral  limestone  regularly  overlying  the  upper  beds  of  the  Primal  slate,  con- 
taining or  consisting  of  the  ore.  * * * In  this  mine,  as  in  that  of  Cornwall 

and  that  of  Lebanon,  some  of  the  ore  contains  a small  amount  of  copper. 


Fig.  11. — East-west  structure  section,  Jones  mine  (along  line  A-B,  Pi.  XVIII). 


A large-scale  topographic  map  of  the  vicinity  of  the  mines  by  J.  H. 
Harden  (reproduced  here  as  PL  XVIII)  accompanies  the  report  by 
D’Invilliers  on  the  geology  of  Berks  County,  but  no  description  of 
tlie  mine  is  given  in  the  text.  However,  something  of  the  geology  and 
structure  of  the  mines  is  indicated  in  cross  sections  which  accompany 
the  map.  These  data  have  been  used  in  constructing  the  revised  cross 
sections  here  given  (figs.  11,  12,  and  13). 

The  Jones  mine  and  the  smaller  Kinney  mine  adjacent  lie  in  the 
isolated  area  of  Paleozoic  limy  strata,  which  are  supposed  to  belong 
near  the  base  of  limestone  “ No.  II  ” of  the  Pennsylvania  section.  As 
at  Boyertown  and  Cornwall,  there  is  apparently  interbedding  of  lime- 
stone and  limy  shale,  the  latter  being  largely  changed  to  ore,  while  the 
former  exhibits  a very  moderate  degree  of  meta  morphism.  Though 
the  pit  is  now  flooded,  it  is  known  from  dips  recorded  on  the  Harden 
map  that  in  the  Jones  workings  the  ore  strata  are  considerably  con- 


Geology  of  Pennsylvania,  vol.  1,  1858,  p.  182. 


GEOLOGICAL  SURVEY 


SKETCH  MAP  SHOWING  GEOLOGY  IN  VICINITY  OF  JONES  AND  WARWICK  MINES,  BERKS  AND  CHESTER  COUNTIES,  PA. 


BERKS  COUNTY  DEPOSITS. 


67 


torted,  the  general  direction  of  dip,  however,  being 
toward  the  west-northwest.  In  the  northern  pit 
the  ore  dips  16°  N.  55°  W.  “Above  the  ore  is  a 
limestone  bed  conformable  to  it,  about  12  to  15  feet 
thick,  and  above  that  still  is  a conformable  light- 
green  earthy  shale.”  0 

The  ore-bearing  strata  are  overlapped  on  the 
north  by  reddish  Mesozoic  conglomerate,  contain- 
ing large  quartzite  pebbles.  East  of  the  large 
mine  the  nature  of  the  bed  rock  can  not  be  deter- 
mined, but  presumably  the  limy  strata  run  out 
for  several  miles  in  this  direction.  On  the  State 
Survey  geologic  map  of  Berks  County  the  “ No. 
II  ” limestone  is  represented  as  a narrow  strip  ex- 
tending through  the  Jones  mine  toward  the  east- 
northeast  as  far  as  Hopewell  furnace,  and  though 
no  outcrops  are  to  be  found  it  is  very  likely  that 
these  strata  underlie  the  accumulation  of  surface 
debris  along  the  topographic  depression  which 
separates  the  red  conglomerate  and  sandstone  hills 
on  the  north  from  the  quartzite  hills  on  the 
south. 

Two  bodies  of  diabase  occur  on  the  south  side  of 
the  Jones  pit  and  are  exposed  along  the  edge  of 
the  excavation.  Between  them  are  limy  strata  in 
the  southwest  corner  of  the  pit,  and  these  beds  prob- 
ably extend  through  to  the  Kinney  mine.  South 
of  the  Kinney  pit  quartzite  fragments  occur  in 
the  soil,  and  near  the  railroad  crossing  this  rock 
may  be  seen  in  place.  It  is  not  known  whether  the 
quartzite  belongs  to  the  Mesozoic  or  to  the  Paleo- 
zoic* “No.  I”  sandstone.  The  area  which  it  occu- 
pies is  limited  on  the  west  and  east  by  the  masses 
of  diabase.  The  western  mass  is  exposed  along 
the  railroad  for  about  one-half  mile;  the  other 
may  be  traced  eastward  to  the  falls  of  French 
Creek  and  for  several  miles  beyond.  The  mass  of 
diabase  represented  on  the  Berks  County  map  just 
north  of  Joanna  station  was.  not  visited  by  the 
writer.  Several  minor  masses  of  diabase,  divid- 
ing the  ore,  were  encountered  in  the  mine  work- 
ings. The  sketch  map  (PI.  XVII)  shows  the 
distribution  of  the  various  rocks  in  the  vicinity  of 
the  Jones  and  Warwick  mines. 


“ Willis,  Bailey,  Tenth  Census,  vol.  15,  1886,  p.  225. 


68 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


The  iron  minerals  of  the  Jones  ore  are  magnetite  and  pyrite,  and 
some  of  the  ore  contains  chalcopyrite.  In  the  richer  material  the 
magnetite  and  pyrite  occur  in  more  or  less  crystalline  form,  accom- 
panied by  calcite  or  dolomite,  the  whole  forming  a rather  granular 
aggregate.  Such  ore  does  not  betray  its  origin ; but  lean  material,  of 
which  there  is  a great  amount  on  the  old  dumps,  shows  clearly  that 
the  iron  minerals  have  been  formed  by  a chemical  substitution  or 
replacement  of  limy  strata.  Blocks  may  be  seen  showing  all  degrees 
of  replacement  and  still  retaining  their  stratification.  Brecciation 
and  cross  veining,  which  are  noteworthy  features  at  Cornwall,  are 
not  observed  in  the  material  from  the  Jones  mine.  As  at  Cornwall, 
chlorite  is  an  abundant  mineral  in  the  waste,  but  only  minor  amounts 
of  this  mineral  occur  in  the  usable  ore.  A few  blocks  of  limestone 
containing  small  garnets  were  noted. 

The  important  role  of  the  intrusive  diabase  as  an  element  in  the 
local  geology  is  shown  by  the  extent  of  the  rocks  indicated  on  the 
geologic  sketch  map  (PI.  XVII).  The  writer  believes  that  the  seg- 
regation of  the  ore  resulted  from  the  intrusion  of  this  rock,  though 
evidence  sufficient  to  establish  this  theory  has  not  been  found.  That 

ore  minerals  were  being  de- 
posited after  the  diabase  had 
been  injected  is  indicated  by 
the  presence  of  magnetite, 
pyrite,  calcite,  and  chlorite  in 
cracks  in  the  igneous  rock  and 
entirely  surrounding  fragments 
of  it.  Blocks  showing  these  relations,  which  presumably  came  from 
one  of  the  minor  masses  of  diabase  encountered  in  the  workings, 
were  found  near  the  engine  house,  on  the  north  side  of  the  Jones  mine. 

From  existing  descriptions  it  appears  that  the  overlapping  Meso- 
zoic strata  are  separated  from  the  ore  body  by  barren  shale  and  lime- 
stone, a relation  which  makes  it  difficult  to  believe  that  the  leaching 
of  these  ferruginous  sediments  could  have  furnished  the  iron  for  this 
large  ore  body  and  which  leaves  the  way  open  for  the  suggestion  that 
the  diabase  was  the  source  of  the  mineralizing  waters  and  of  the  iron 
that  they  contained. 

The  discussion  of  the  possible  occurrence  of  other  ore  deposits  in 
the  vicinity  will  be  deferred  until  the  detailed  geologic  map  of  the 
district  is  available.  Professor  Bascom,  of  Bryn  Mawr  College,  is 
now  engaged  in  studying  the  geology  of  the  Honeybrook  quadrangle, 
in  which  the  mines  are  situated. 

The  following  note  is  copied  from  Frazer:0 

On  the  lands  of  the  Warwick  reserve,  2 miles  southeast  of  the  Joanna  furnace 
and  about  li  miles  east  of  Morgantown  and  4 mile  south  of  the  narrow  belt  of 


Fig.  13. — East-west  structure  section,  Kinney 
mine  (along  line  E-F,  PI.  XVIII). 


a Frazer,  Persifor,  jr.,  Second  Geol.  Survey  Pennsylvania,  Rept.  CCC,  1877,  p.  237. 


u.  S.  GEOLOGICAL  SURVEY  BULLETIN  NO.  359  PL.  XVII. 


TOPOGRAPHIC  MAP  OF  VICINITY  OF  JONES  AND  KINNEY  MINES,  BERKS  COUNTY,  PA. 


BERKS  COUNTY  DEPOSITS. 


69 


limestone  which  leaves  the  large  Lancaster  limestone  tract  and  passes  through 
Morgantown,  * * * in  Berks  County,  is  an  exploitation  for  ore..  * * * 

The  material  thrown  out  of  the  pit  appears  to  be  an  altered  mud  rock,  along- 
side of  which  occurs  ore  very  like  that  of  Cornwall  and  some  of  that  from 
Dillsburg. 

WARWICK  MINE. 

The  old  workings  of  the  Chester  County  Warwick  mine  are  situ- 
ated just  east  of  Warwick,  formerly  known  as  St.  Marys.  (See  PI. 
XVII.)  The  deposit  appears  to  have  been  nearly  exhausted  prior 
to  1875,  although  there  was  some  mining  as  late  as  1882.  Little  can 
be  made  out  by  an  examination  of  the  ground  at  the  present  time,  but 
such  features  as  can  be  observed  correspond  with  the  following  de- 
scription published  by  II.  D.  Rogers  in  1858 : ° 

This  extensive  and  interesting  body  of  iron  ore,  situated  just  southeast  of 
St.  Mary’s  Episcopal  Church,  is  in  reality  not  a genuine  lode  or  igneous  intru- 
sive vein,  though  the  ore  derives  some  of  its  characters  from  intrusive  igneous 
action,  but  it  is  a bed  or  deposit  at  the  base  or  very  near  the  base  of  the  middle 
secondary  red  sandstone,  which  here  laps  upon  the  gneiss.  The  explored  extent 
of  this  bed,  hitherto  penetrated  only  near  its  outcrop,  or  where  the  overlying 


N 


Fig.  14. — Structure  section  at  Warwick  mine,  Chester  County.  After  H.  D.  Rogers. 

1,  Diabase ; 2,  gneiss. 


strata  are  shallow,  is  already  very  great,  amounting  to  many  acres.  The  ore 
deposit  observes  everywhere  a very  gentle  dip,  and  seems  to  undulate  in  two 
or  three  waves  across  the  tract  which  includes  it.  A somewhat  conspicuous 
anticlinal  change  in  the  dip  occurs  to  the  south  and  southwest  of  the  present 
main  engine  shaft  by  which  the  mines  are  dried,  and  there  is  every  indication 
that  the  ore  basins  are  both  south  and  north  of  this  saddle.  Though  the  basin 
to  the  south  of  it  is  intersected,  and  the  ore  in  one  place  cut  off  or  thrown  out 
to  the  surface  by  the  intrusion  of  a wide  dike  of  trap  rock,  there  is  strong 
reason  to  infer  that  the  ore  occupies  a comparatively  wide  though  perhaps 
shallow  basin,  north  and  northeast  of  the  engine  shaft  [fig.  14]. 

Besides  this  intrusion  of  trap,  there  seems  to  exist  here  injections  of  serpen- 
tine and  other  mineral  matters,  and  at  one  point,  just  by  the  southwest  margin 
of  the  ore  bed,  there  exists  a very  singular  intrusion  of  mineral  matter  pene- 
trating the  ore  and  altering,  in  a remarkable  manner,  the  conglomeratic  layers 
which  here  constitute  the  southeast  border  of  the  red  sandstone  formation. 
This  rock  is  greatly  baked  and  changed  in  aspect,  includes  numerous  spheroidal 
bunches  of  segregated  crystalline  mineral  matters  (some  of  them  in  the  form 
of  hollow  geodes),  and  is  intersected  besides  with  numerous  strings,  or  little 
veins.  In  these  spheroidal  nests  occur  beautiful  linings  of  crystallized  epidote 
and  other  minerals,  and  bunches  of  large  crystals  of  the  fine  variety  of  garnet 
called  melenite.  The  list  of  the  minerals  occurring  here  is  not  extensive.  The 


Geology  of  Pennsylvania,  vol.  2,  1858,  pp.  708-709. 


70 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


conditions  under  which  they  present  themselves  are  such  as  strongly  to  impress 
the  geological  observer  with  the  notion  of  their  having  been  introduced  chiefly 
in  a vaporous  state,  or  by  sublimation,  for  in  many  of  these  hollow  spheroids 
we  can  detect  no  connection  whatever  between  the  interior  or  even  the  exterior 
walls  of  the  geodes  and  any  external  veins  or  filaments  of  injected  matter,  such 
as  any  other  theory  would  demand  for  the  introduction  of  the  materials  of  the 
crystalline  minerals  here  so  curiously  insulated. 

The  bed  of  iron  ore  for  which  this  locality  is  chiefly  noted  is  of  very  variable 
thickness,  fluctuating  from  1 or  2 to  9 or  even  17  feet.  As  illustrating  the 
general  levelness  of  this  undulating  deposit,  it  may  be  stated  that  in  no  place 
has  it  been  required  to  sink  deeper  than  about  60  feet  to  reach  the  ore,  while 
generally  the  covering  is  so  thin  that  the  ore  is  conveniently  procured  by  merely 
stripping  off  a thickness  of  a few  feet  or  yards  of  loose  disintegrated  rock.  The 
average  richness  of  this  ore  may  be  stated  at  about  45  per  cent  of  metallic 
iron,  though  much  of  it  exceeds  50  per  cent.  It  is  somewhat  sulphurous ; and 
when  care  is  not  employed  in  selecting  it  for  smelting,  and  in  the  after 
processes,  it  tends  to  produce  n hot-short  or  red-short  iron,  but  when  carefully 
manufactured  it  yields  an  excellent  metal.  The  annual  product  of  the  Warwick 
iron  mines  for  fifteen  years  was  not  less  than  4,000  tons,  and  the  average  yield 
for  the  past  twenty  years  has  been  6,000  tons.  In  the  year  1853  the  amount 
mined  reached  12,000  tons.  These  ore  pits  have  been  wrought  for  the  last  one 
hundred  and  twenty  years,  and  there  would  seem  to  be  at  present  really  more 
ore  within  sight  than  there  has  ever  been  before  at  any  one  time.  The  present 
average  cost  of  mining  this  ore  is  about  $1.50  per  ton.  * * * 

This  ore  is  intermediate  in  its  physical  characters  and  aspect  between  the 
true  brown  hematite  and  the  magnetic  oxide  of  iron.  As,  on  the  view  of  its 
having  been  originally  hematite  but  subsequently  altered  by  igneous  action,  we 
might  naturally  anticipate,  those  portions  of  it  which  have  undergone  the  high- 
est degree  of  metamorphic  influence  are  of  a gray  color,  quite  crystalline,  and 
partially  endowed  with  magnetic  force,  whereas  the  less  altered  parts  are  nearly 
in  the  condition  of  a compact,  closely  cemented  hematite.  Minutely  interstrati 
fled  with  this  ore  there  occurs  more  or  less  earthy  matter,  apparently  laminae 
of  indurated  slate  or  shale ; and  when  the  layers  of  this  rock  are  thick,  and  they 
disperse  the  ore,  they  interfere  materially  with  the  economical  prosecution  of 
the  mine.  This  slaty  or  earthy  matter  tends,  furthermore,  by  intimately  mixing 
itself  in  with  the  finer  granular  ore,  seriously  to  reduce  the  richness  of  the 
mingled  mass  in  iron. 

Specimens  of  the  metamorphosed  conglomerate  described  by  Rogers 
may  be  found  in  the  old  mine  pits..  Green  hornblende  and  brown 
garnet,  calcite,  pyrite,  specular  hematite,  and  magnetite  are  among 
the  secondary  minerals  observed.  Epidote  Avas  not  noted.  No  geol- 
ogist familiar  with  the  common  metamorphic  alterations  of  sedi- 
mentary rocks  adjacent  to  intrusive  igneous  masses  can  see  this 
material  without  regarding  it  as  a product  of  contact  metamorphism 
iiwolving  the  action  of  heated  water.  In  the  Avriter’s  opinion  the 
features  of  the  ore  specimens  which  have  been  examined  do  not  sug- 
gest that  the  magnetite  of  the  Warwick  deposit  has  been  produced 
from  broAvn  hematite  by  heat  metamorphism,  as  proposed  by  Rogers, 
but  it  seems  that  hematite,  magnetite,  and  pyrite  must  have  been 
introduced  into  their  present  situation  and  must  have  been  formed 
contemporaneously. 


YORK  COUNTY  DEPOSITS. 


71 


In  conformity  with  the  general  theory  concerning  the  origin  of 
other  deposits  of  the  Cornwall  type,  it  is  suggested  that  the  ore  min- 
erals were  introduced  by  solutions  sent  into  circulation  by  the  in- 
trusive diabase  that  occurs  north  of  the  mines.  This  view  is  justified 
by  the  baked  condition-  of  the  Mesozoic  strata  throughout  the  strip 
which  lies  south  of  the  diabase  mass  and  by  the  observed  alteration 
of  the  conglomerate  rock,  so  well  described  by  Rogers.  There  is  no 
evidence  to  show  whether  the  iron  was  leached  out  of  the  Mesozoic 
strata  or  was  furnished  by  the  igneous  rock. 

The  geologic  relations  observed  at  the  Warwick  mines  continue  for 
some  distance  both  east  and  west.  It  is  thought  not  improbable  that 
similar  ore  deposits  may  exist  at  other  points,  between  the  east-west 
mass  of  diabase  and  the  south  edge  of  the  Mesozoic  strip  which  marks 
the  overlap  of  the  sandstone  upon  the  ancient  gneisses.  Bodies  of 
iron  ore  may  lie  in  a position  similar  to  that  of  the  Warwick  deposit 
and  still  not  extend  far  enough  south  to  have  been  brought  to  light 
along  the  edge  of  the  Mesozoic  strip.  If  erosion  had  been  only 
slightly  less  than  what  is  actually  observed  in  the  neighborhood  of 
the  old  mines  the  edge  of  the  ore  deposit  would  not  have  been  stripped 
of  its  cover  and  would  not  have  been  discovered  except  by  some 
chance  excavation  of  considerable  depth.  On  the  other  hand,  the 
removal  of  a little  more  cover  elsewhere  along  the  line  of  overlap 
might  have  revealed  deposits  similarly  situated,  of  which,  under  ex- 
isting conditions,  there  are  no  surface  indications.  Although  it  is 
regarded  as  possible  that  systematic  drilling  might  lead  to  the  discov- 
ery of  new  ore  deposits  in  the  ground  indicated,  the  undertaking  of 
such  extensive  explorations  as  would  be  required  can  hardly  be  rec- 
ommended as  a business  venture  at  the  present  time. 

About  2^  miles  east  of  the  Warwick  mines  and  just  north  of 
Knauertown  indications  of  iron  ore  were  prospected  many  }^ears  ago. 
The  geologic  position  is  identical  with  that  of  the  Warwick  deposit. 
On  the  basis  of  the  theory  that  the  mass  of  diabase  which  lies  north 
of  this  place  has  been  the  inciting  cause  of  the  deposition  of  iron  min- 
erals, it  is  not  unreasonable  to  expect  that  these  indications  may  lead 
to  a better  deposit  of  ore  at  a greater  depth  beneath  the  hill. 

YORK  COUNTY  DEPOSITS. 

GENERAL  STATEMENT. 

Iron  ores  like  those  of  the  Cornwall  mines  occur  at  several  locali- 
ties in  northern  York  County.  The  principal  group  of  mines  is  sit- 
uated about  1 mile  east  of  Dillsburg,  and  a second  smaller  group  is 
located  just  south  of  Yellow  Breeches  Creek  near  Grantham  crossing, 
on  the  Philadelphia  and  Reading  Railroad.  Specular  hematite  with 
some  associated  magnetite  has  been  worked  at  Minebank  schoolhouse, 


72 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


about  2 miles  southwest  of  Wellsville,  and  minor  pockets  and  indica- 
tions of  ore  have  been  found  at  various  other  localities.  Most  of 
these  occurrences  had  been  discovered  prior  to  1873  and  are  described 
or  mentioned  in  Report  CC  of  the  Second  Geological  Survey  of 
Pennsylvania  ° and  in  the  Annual  Report-  for  1886.6 

In  1907,  when  the  writer  visited  the  field,  no  mining  was  being 
done,  so  that  such  data  as  could  be  collected  concerning  these  interest- 
ing deposits  have  been  procured  from  examinations  of  the  surface 
and  from  conversation  with  persons  familiar  with  the  underground 
operations.  Since  the  publication  of  the  reports  mentioned  above 
only  two  new  mines  have  been  opened,  but  considerable  ore  has  been 
taken  from  several  of  the  old  ones. 

Two  opinions  have  been  expressed  in  published  descriptions  re- 
garding the  geologic  position  of  the  Dillsburg  deposits.  They  have 
been  held  on  the  one  hand  to  lie  in  Mesozoic  rocks  and  on  the  other  to 
occur  in  Paleozoic  strata,  as  at  Cornwall.  Detailed  study  of  the  gen- 
eral region  now  shows  that  all  the  deposits  are  inclosed  by  the  younger 
set  of  rocks,  as  stated  by  D’Invilliers. 

The  Grantham  mines  lie  very  near  the  edge  of  the  Mesozoic  area ; 
those  of  the  Dillsburg  group  are  situated  from  1^  to  2J  miles  within 
the  northwest  boundary,  and  the  mine  southwest  of  Wellsville  lies  6J 
miles  within  the  Mesozoic  belt.  (See  PI.  XIX.)  No  bodies  of  ore 
and  no  strong  indications  of  ore  occurrence  have  been  found  except 
where  the  strata  have  been  greatly  metamorphosed  or  baked  in  prox- 
imity to  intrusive  masses  of  diabase.  This  association  points  defi- 
nitely, as  do  all  other  occurrences  of  iron  ore  of  the  Cornwall  type,  to 
the  belief  that  the  ores  are  connected  in  origin  with  the  intrusion  of 
the  diabase.  However,  the  mere  presence  of  diabase  in  a locality  is 
by  no  means  sufficient  to  insure  the  presence  of  ore  near  by ; otherwise, 
York  County  would  be  unsurpassed  as  an  ore  field  because  of  the 
great  extent  of  the  diabase  masses  within  her  borders.  The  scattered 
or  limited  occurrence  of  ore  deposits  points  to  a second  condition  as 
essential  to  the  formation  of  ore,  and  it  is  believed  that  this  condition 
is  the  presence  of  calcareous  (or  lime-bearing)  rocks  in  the  vicinity 
of  intrusive  masses  of  diabase.  In  all  the  more  important  mines  of 
the  Dillsburg  group  and  at  Grantham  beds  of  limestone  conglomerate 
are  found  in  the  workings.  At  Minebank,  also,  crystallized  limestone 
is  to  be  found  in  the  mine  waste.  At  Dillsburg  many  pockets  of  ore 
which  were  mined  out  years  ago  and  one  bed  continuous  for  nearly 
500  feet  at  the  surface  (McCormick  long  cut)  appear  to  have  been 
inclosed  in  baked  sandstone.  Though  there  is  now  no  evidence  that 
limestone  occurs  in  these  workings,  it  is  possible  that  the  masses  of 

° Frazer,  Persifor,  jr.,  Report  of  progress  in  the  counties  of  York,  Adams,  Cumber- 
land. and  Franklin.  1877,  pp.  201  -239. 

"Ann.  Kept.  Geol.  Survey  Pennsylvania  for  188G,  pt.  4,  1887,  pp.  17)01-1514. 


GEOLOGICAL  SURVEY 


77*00* 


older 


YP-' 

Or.tnllmnt' 


f*Siddonsbur| 


randtsville 


_-»kyMQn{^}iap_  jlQ.- 


Paleozoic 


older 


-Uno' 


rSteyetisttown. 


§gp§ 

llossvllk' 


^Mount^  Top ' 


Mesozoic  red  sandstones 
and  shales 


Limestone  conglomerate 
(This  rock  occurs  in 
several  of  the  mines) 


Mines  and  prospects 


GEOLOGIC  SKETCH  MAP  OF  MESOZOIC  AREA  NEAR  DILLSBURG,  YORK  COUNTY,  PA. 


YOKK  COUNTY  DEPOSITS.  73 

ore  represent  original  bodies  of  limestone  conglomerate  which  have 
been  converted  into  iron  ore  by  chemical  replacement. 

In  the  vicinity  of  the  Dillsburg  mines  there  are  no  natural  ex- 
posures of  limestone  conglomerate  and  only  along  the  Philadelphia 
and  Reading  tracks  near  Grantham  can  this  rock  be  seen  at  the  sur- 
face near  known  ore  bodies.  In  drill  holes  near  the  old  McCormick 
workings  at  Dillsburg  the  occurrence  of  limestone  has  been  recorded. 

Exposures  of  rock  in  place  in  this  region  are  very  few  in  number, 
but  the  distribution  of  the  diabase  and  of  the  Mesozoic  rocks  as  a 
whole  can  be  recognized  from  the  presence  of  residual  bowlders  or 
broken  fragments  in  the  soil.  It  is  not  possible,  however,  to  decipher 
any  details  concerning  the  make-up  of  the  sedimentary  formation. 
It  is  supposed  that  there  may  be  several  beds  of  limestone  conglom- 
erate separated  from  each  other  by  sandstone  and  shales,  but  only  the 
presence  of  the  latter  can  be  ascertained  from  inspection  of  the  soil. 
Everywhere  the  materials  of  the  surface  debris  show  evidence  of  the 
baking  which  the  rocks  have  undergone.  The  absence  in  the  vicinity 
of  the  mines  of  fragments  from  the  limestone  conglomerate  is  no 
doubt  due  to  the  great  solubility  of  this  rock  compared  with  the  over- 
wash of  the  more  resistant  baked  sandstone  fragments. 

Limestone  conglomerate  outcrops  at  several  places  west  and  south- 
west of  Dillsburg,  showing  that  here  it  is  an  important  element  in 
the  constitution  of  the  Mesozoic  formation.  In  the  foothills  of  South 
Mountain,  northwest  of  Beavertown,  fully  50  feet  of  the  rock  is  ex- 
posed in  a large  quarry.  This  quarry  has  been  opened  around  a 
sink  hole,  into  which  a small  brook  disappears.  A series  of  sinks 
may  be  followed  from  this  place  for  nearly  a mile  toward  the  north- 
east. Though  the  sink  holes  suggest  that  the  conglomerate  continues 
as  the  bed  rock  in  this  direction  there  are  no  exposures,  because  of  the 
heavy  overwash  derived  from  the  mountain  slope,  and  it  is  possible 
that  a strip  of  the  Paleozoic  limestone  sets  in  between  the  quartzites 
of  South  Mountain  and  the  Mesozoic  beds,  which  lie  to  the  east.  In 
this  situation  either  the  limestone  conglomerate  or  the  older  lime- 
stone would  be  liable  to  contain  underground  watercourses  and  to 
give  rise  to  the  observed  sinks.  At  a quarry  on  the  west  side  of  the 
York  Springs  road,  about  1 mile  from  Dillsburg,  12  or  15  feet  of 
conglomerate  are  seen  lying  between  a stratum  of  red  sandy  shale, 
and  massive  beds  of  metamorphosed  conglomerate  may  be  seen  a 
mile  southwest  of  this  quarry,  at  the  eastern  base  of  the  diabase  hill, 
along  an  abandoned  railroad  grade.  The  same  rock  is  said  to  have 
been  found  in  several  dug  wells  in  the  northern  and  western  parts 
of  Dillsburg.  A drilled  well  at  the  creamery  penetrated  80  feet  of 
conglomerate,  and  at  this  depth  encountered  an  open  cavity.  This 
well  overflows  during  wet  seasons.  The  only  exposure  noted  within 
the  borough  limits  is  just  south  of  the  mine  railroad  at  the  eastern- 


74 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


most  street  crossing.  The  occurrences  which  have  been  mentioned 
strongly  suggest  that  west  of  Dillsburg  the  broad  valley  occupied  by 
Dogwood  Run  and  its  southern  tributaries  is  underlain  by  limestone 
conglomerate.  It  seems  probable  also  that  beds  of  the  same  rock  are 
present  beneath  the  meadows  east  of  Dillsburg,  between  the  town  and 
the  mines.  This  is  suspected  because  the  conglomerate  is  known  to 
occur  both  east  and  west  of  the  flat,  and  because  the  presence  of  this 
soluble  rock  would  be  a favorable  condition  for  the  development  of 
j ust  such  a broad  basin  as  exists. 

It  may  be  mentioned  incidentally  that  the  presence  in  the  soil  of 
debris  derived  from  the  South  Mountain  rocks  showTs  that  Dogwood 
Run  formerly  flowed  across  this  depression  and  joined  Yellow 
Breeches  Creek  by  way  of  Fishers  Run. 

The  geologic  sketch  map  (PI.  XIX)  shows  the  general  position  of 
the  boundary  between  the  Mesozoic  area  and  the  older  formations  of 
South  Mountain,  and  also  the  approximate  distribution  of  the  dia- 
base intrusions  in  the  Dillsburg  region.  The  close  association  of  the 
ore  with  the  masses  of  igneous  rock  is  well  brought  out  by  the  indi- 
cated positions  of  the  mines  and  prospects  of  the  district. 

DILLSBURG  MINES. 

INTRODUCTION. 

The  Dillsburg  ore  field  has  a greater  extent  than  any  of  the  other 
districts  which  furnish  ore  of  the  Cornwall  type.  Ore  has  been  taken 
from  more  than  30  openings,  including  open  pits  and  underground 
mines,  and  these  workings  are  distributed  over  a zone  nearly  1J  miles 
long  and  from  one- fourth  to  one-half  mile  wide. 

The  annual  output  of  the  Dillsburg  mines  has  never  been  large  and 
the  aggregate  of  the  ore  shipped  is  probably  less  than  1,500,000  tons, 
the  period  of  production  having  been  about  sixty  years.  The  ores 
have  not  been  in  general  or  constant  demand,  mainly  because  they 
are  high  in  sulphur,  but  also  because  their  iron  content  is  low  in  com- 
parison with  that  of  Lake  ores.  They  compare  favorably,  however, 
with  the  Cornwall  ore,  the  use  of  which  has  been  on  the  increase  for 
many  years.  Like  the  Cornwall  ore  they  must  be  roasted  before 
going  to  the  blast  furnace,  except  when  they  are  mixed  in  rather  small 
proportions  with  other  ores.  The  fact  that  the  Dillsburg  ore  has 
found  even  a limited  market  at  various  times  during  the  last  twenty 
years  is  sufficient  ground  for  believing  that  if  the  mines  can  be  shown 
to  be  capable  of  further  output  no  serious  difficulty  need  be  expected 
in  disposing  of  the  product.  The  mines  have  been  worked  mainly 
by  individual  owners  and  lessees  without  sufficient  capital  to  carry 
development  far  enough  ahead  of  extraction  to  justify  operation  on 
a large  scale.  Could  the  ore  fields  be  brought  under  the  control  of 


YORK  COUNTY  DEPOSITS. 


75 


interests  strong  enough  to  explore  the  deposits  adequately  and,  if  pre- 
liminary work  should  warrant,  to  develop  them  on  a large  scale,  it 
seems  likely  that  they  might  be  brought  again  into  successful  opera- 
tion. Even  a moderate  tonnage,  if  assured  for  a period  of  years, 
might  warrant  the  maintenance  of  roasting  furnaces,  or,  what  might 
prove  more  advantageous,  the  installation  of  some  concentrating 
process  to  raise  the  grade  of  the  ore  as  it  comes  from  the  mine.  Geo- 
logic considerations  favor  the  persistence  of  the  deposits  in  depth  and 
point  to  the  probability  that  ore  bodies  in  addition  to  those  now 
known  might  be  discovered  by  systematic  prospecting. 

It  is  hoped  that  the  present  description  and  the  geologic  map  of 
the  district  (PL  XX)  that  has  been  prepared  may  aid  in  the  future 
development  of  the  deposits. 

DESCRIPTIONS  OF  MINES. 

Logan  mine. — The  shaft  of  the  Logan  mine,  which  is  the  most  re- 
cent opening  in  the  district,  is  located  about  200  feet  north  of  the 
wagon  road  leading  from  Dillsburg  to  Stevenstown.  It  is  situated 
just  within  the  outcrop  of  a diabase  sill  about  200  feet  wide,  which 
crosses  the  road  east  of  the  forks.  Mr.  Logan,  the  owner  of  the 
property,  was  encouraged  to  open  at  this  place  through  having  ob- 
served a strong  magnetic  attraction  determined  with  a dipping 
needle.  The  bottom  of  the  diabase  is  evidently  inclined  toward  the 
north  at  a low  angle,  for  it  is  said  to  have  been  penetrated  at  a depth 
of  32  feet.  Mr.  Logan  reports  that  7 feet  of  ore  was  encountered 
just  under  the  diabase,  and  that  the  floor  is  limestone  conglomerate. 
The  ore  bed  and  the  inclosing  rocks  dip  toward  the  north.  The 
mine  was  operated  for  a short  time  only,  so  that  the  extent  of  the  ore 
body  is  not  known. 

Xorth  of  the  shaft  the  surface  slopes  gently  toward  a small  stream 
fed  by  a spring  between  the  two  forks  of  the  wagon  road.  Sand- 
stone fragments  observed  along  the  depression  occupied  by  this  stream 
indicate  the  presence  of  a strip  of  sedimentary  rock,  which,  as  it  is 
traced  toward  the  east,  curves  to  the  south  and  crosses  the  right-hand 
road  just  wTest  of  the  church.  It  is  thought  that  this  band  of  sand- 
stone may  run  dowm  the  ravine  and  across  Fishers  Pun  to  join  a 
similar  band  which  sets  in  from  the  west,  but  this  connection  can  not 
be  established  from  observation.  Xorth  of  the  sedimentary  strip 
diabase  appears  at  the  surface  and  continues  without  interruption  to 
the  vicinity  of  the  Jauss  and  King  mines. 

South  of  the  diabase  intrusion  penetrated  by  the  Logan  shaft  there 
is  a considerable  strip  of  sedimentary  rock,  beyond  which  appears 
another  somewhat  wider  diabase  band.  These  two  masses  of  diabase 
come  together  southeast  of  the  mine.  Still  farther  south  there  is  yet 
another  band  of  sedimentary  rock,  and  beyond  this  is  the  large  mass 


76 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


of  diabase  forming  the  group  of  hills  south  and  east  of  Stevenstown. 
As  already  noted,  this  diabase  extends  westward  to  Dillsburg. 

Inasmuch  as  limestone  conglomerate  occurs  at  the  old  Price  pit, 
and  also  in  the  Logan  mine  1,300  feet  to  the  east,  there  is  reason 
to  believe  that  the  mass  of  diabase  which  lies  immediately  north  of 
both  mines  is  a sill  conforming  more  or  less  closely  with  the  stratifi- 
cation of  the  sedimentary  rock  into  which  it  has  been  injected.  The 
limestone  conglomerate  dissolves  under  the  action  of  the  weather,  so 
that  its  presence  can  not  be  determined  by  inspection  of  the  surface 
debris.  It  is  very  likely  that  it  extends  along  the  contact  with  the 
diabase  between  the  Logan  and  Cox  openings,  and  west  of  the  Price 
pit,  perhaps  as  far  as  the  .next  north-south  wagon  road.  There  is 
nothing  to  suggest  how  far  it  may  extend  toward  the  east  and  south- 
east beneath  the  diabase  sill. 

The  masses  of  diabase  occurring  south  of  the  Logan  mine  are  prob- 
ably sills,  and  other  beds  of  conglomerate  may  be  associated  with 
them.  If  this  is  the  case,  it  seems  very  likely  that  other  ore  deposits 
may  be  present  in  the  country  south  of  the  Price,  Cox,  and  Logan 
mines.  Though  it  may  be  suggested  that  surface  indications  should 
betray  the  presence  of  any  considerable  deposit  of  ore  in  this  part  of 
the  district,  the  surface  debris  is  here  apparently  so  thick  and  so 
liable  to  have  moved  for  some  distance  that  the  weathered  portions 
of  ore  beds  might  very  well  have  been  entirely  covered.  This  is 
particularly  true  of  the  strip  of  sedimentary  rocks  which  lies  north  of 
the  Logan  shaft.  Both  sides  of  this  strip  would  seem  to  offer  likely 
situations  for  the  occurrence  of  iron-ore  deposits.  The  Logan  ore 
was  discovered  by  means  of  the  dipping  needle.  This  instrument  may 
prove  of  value  in  further  exploration  of  this  ground. 

Cox  mine. — The  Cox  mine  is  situated  about  950  feet  west  of  the 
Logan  shaft,  just  south  of  the  same  diabase  sill.  The  mine  was  in  op- 
eration when  the  Dillsburg  field  was  visited  by  D’Invilliers,  whose 
report  ° may  be  summarized  as  follows : 

At  the  Cox  mine,  on  the  Price  farm,  the  engine  house  is  situated 
just  north  of  the  public  road.  The  ore  bed  is  mined  by  means  of  a 
slope  about  300  feet  long  on  a bed  of  magnetic  ore  dipping  about  25° 
a little  west  of  north.  Near  by  is  an  abandoned  slope  descending 
nearly  due  north  for  280  feet,  and  in  a shaft  125  feet  north  of  the 
engine  house  the  ore  bed  was  struck  near  this  slope  at  a depth  of 
about  40  feet.  The  ore  so  far  as  developed  seems  to  lie  in  a deposit 
shaped  like  a shell,  the  top  and  bottom  of  the  shell  coming  together 
and  pinching  out  the  ore  on  all  sides  along  the  strike,  as  well  as  along 
the  dip.  The  average  thickness  of  the  bed  is  54  to  6 feet,  though  in 
places  it  swells  to  9 feet.  Generally  it  has  a gray  dolerite  trap  for  a 
hanging  wall  and  a sandy  bastard  limestone  for  a foot  wall;  but 


“ Ann.  Kept.  Geol.  Survey  Pennsylvania  for  1886,  pt.  4,  p.  1504. 


YORK  COUNTY  DEPOSITS. 


77 


there  seems  to  be  no  very  persistent  character  for  either.  The  west- 
ern side  of  the  deposit  is  more  mixed  in  character  than  the  eastern, 
and  in  places  the  trap  wall  seems  to  stand  almost  vertical,  squeezing 
the  ore  into  a narrow  compass.  The  foot  wall  in  many  places  ap- 
pears more  like  white  baked  slate  rock  than  like  limestone,  but  con- 
tains some  lime.  In  April,  1887,  ore  was  being  mined  at  the  rate  of 
25  tons  per  day. 

West  of  the  slope  a small  open  cut  exhibits  a bed  of  rather  sandy 
ore,  from  which  perhaps  200  tons  have  been  taken. 

Price  mine. — A large  pit  situated  about  250  feet  west  of  the  Cox 
slope  is  known  as  the  Price  mine.  The  mine  is  said  to  have  been 
opened  about  1855  and  the  ore  is  reported  to  have  been  6 feet  thick. 
Fragments  of  limestone  conglomerate  may  be  seen  in  a small  pile  of 
waste  in  the  pit.  The  edge  of  the  diabase  sill  passes  just  north  of 
the  pit  and  the  dip  of  the  rocks  is  evidently  toward  the  north,  as  at 
the  Logan  shaft  and  Cox  slope.  Instead  of  being  in  actual  contact 
with  the  diabase  the  ore  body  appears  to  have  been  separated  from 
the  mass  of  igneous  rock  by  intervening  beds  of  sedimentary  rock. 
The  sedimentary  area  between  the  two  sills  of  diabase  is  much  nar- 
rower in  the  vicinity  of  the  Price  mine  than  farther  east.  The 
southern  sill  comes  to  a blunt  termination  in  the  field  northwest  of 
and  across  the  road  from  the  schoolhouse. 

Grove  mine. — About  1,400  feet  due  west  of  the  Price  pit  is  the  mouth 
of  the  Grove  slope,  which  was  opened  in  1873.  The  dip  of  the  rocks 
is  given  in  Report  CC  as  24°  N.  10°  E.  Though  rock  resembling 
weathered  trap  is  said  to  occur  at  the  mouth  of  the  slope,  the  present 
writer  was  not  able  to  find  any  evidence  of  other  material  than  sand- 
stone and  shale  in  the  vicinity.  In  the  wagon  road  north  of  the 
opening  exposures  of  baked  shale  are  to  be  seen  dipping  about  20°  N". 

About  400  feet  south  of  the  slope  is  an  old  excavation,  doubtless  an 
ore  pit,  but  no  information  has  been  procured  concerning  what  was 
found  at  this  place  or  when  the  opening  was  made.  The  edge  of  the 
east-west  diabase  mass  passes  about  300  feet  south  of  the  pit. 

Prospects  near  the  Price  farmhouse. — Mr.  Logan,  the  present  owner 
of  the  Price  farm,  states  that  a bore  hole  put  down  in  the  swamp  east 
of  the  farmhouse  encountered  ore  at  a depth  of  75  feet.  This  hole  ap- 
pears to  have  been  located  north  of  the  boundary  of  the  main  mass 
of  diabase,  and  the  ore  probably  lies  on  the  under  contact  of  the  in- 
trusive rock.  Inspection  of  the  geologic  map  will  show  the  position 
of  this  occurrence  with  reference  to  the  strip  of  sedimentary  rock 
occurring  north  of  the  Logan  mine.  It  seems  that  if  the  diabase  con- 
tact follows  the  stratification  in  this  vicinity  ore  may  occur  to  the  east 
as  well  as  near  the  Price  house,  although,  as  stated  previously,  the 
continuity  of  the  sedimentary  strip  across  the  creek  is  not  proved. 


78 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Indications  of  ore  have  been  found  700  feet  northwest  of  the  farm- 
house, just  at  the  edge  of  the  diabase,  where  the  boundary  curves 
toward  the  north.  No  other  signs  of  ore  are  known  to  have  been 
found  between  this  point  and  the  Bell  mine. 

Bell  mine. — The  Bell  mine,  which  was  opened  in  1875,  is  situated 
about  midway  between  the  Price  pit  and  the  Underwood  group  of 
workings.  It  was  last  worked  about  1902,  at  which  time  the  pillars 
of  ore  were  robbed  and  the  mine  finally  abandoned.  From  a statement 
by  Frazer®  that  bowlders  of  hard  limestone  were  encountered  in  the 
upper  25  feet  of  the  discovery  shaft  just  north  of  the  entrance  to  the 
working  slope,  it  is  judged  that  the  ore  lies  beneath  limestone  con- 
glomerate. This  suggestion  is  corroborated  by  the  presence  of  con- 
glomerate in  the  mine  waste,  but  there  can  be  little  doubt  that  the 
mass  of  diabase  lies  at  no  great  distance  above  the  ore  body. 


Fig.  15. — Plan  and  sections  of  Bell  mine,  near  Dillsburg.  From  Ann.  Kept.  Pennsyl- 
vania Geol.  Survey  for  1885,  p.  566. 


The  mine  was  worked  by  a slope  a short  distance  south  of  the  main 
diabase  area.  The  course  of  the  slope  is  N.  10°  E.  and  its  inclination 
is  said  to  be  about  20°,  though  the  cross  section  given  in  fig.  15  indi- 
cates a lower  angle  of  inclination.  In  1883  the  slope  was  about  875 
feet  long,  but  it  was  afterward  extended  200  feet  or  more.  The  ore 
body  is  said  to  have  had  the  form  of  a rather  well-defined  shoot  fol- 
lowing the  dip  of  the  inclosing  strata,  but  limited  on  both  sides  along 
the  strike.  The  maximum  width  is  stated  by  D’lnvilliers  b to  have 
been  GO  feet,  and  at  875  feet  from  the  mouth  of  the  slope  the  bed  was 
10  to  12  feet  thick.  In  fig.  15  the  ore  is  shown  to  be  cut  out  on  the 
east  by  diabase  (see  PL  XX),  and  from  the  relations  shown  it  may 


a Frazer,  Persifor,  jr.,  Second  Geol.  Survey  Pennsylvania,  Rept.  CC,  1877,  p.  218. 
6 Ann.  Rept.  Geol.  Survey  Pennsylvania,  pt.  4,  for  1886,  1887,  p.  .1505. 


YORK  COUNTY  DEPOSITS. 


79 


Fig.  16. — Surface  plan  at  Bell  mine,  near  Dillsburg, 
showing  probable  structure. 

This  point  may  be  worthy  of  investi- 


be  that  the  ore  body  occurs  adjacent  to  a roll  in  the  bottom  of  the 
diabase  mass  where  this  rock  locally  cuts  across  the  strata  (fig.  16). 
The  course  of  the  diabase  boundary  at  the  surface  is  favorable  to 
this  suggestion. 

If  the  suggested  structure  is  borne  out  by  the  facts,  it  is  not  likely 
that  other  ore  bodies  exist 
toward  the  east,  where  dia- 
base would  be  encountered, 
nor  toward  the  west,  where, 
though  present,  the  ore- 
bearing  stratum  is  prob- 
ably not  mineralized. 

Although  it  is  reported 
that  the  bottom  of  the 
slope  is.  not  in  ore,  it  may 
be  that  one  of  the  sides  of 
the  shoot  has  been  encoun- 
tered rather  than  its  bottom, 
gation  at  some  future  time. 

When  the  mine  was  abandoned  the  slope  was  1,100  feet  in  length. 

About  200  feet  south  of  the  Bell  slope  is  an  old  slope  stated  by 
Frazer  a to  have  been  180  feet  long.  From  a point  125  feet  down  the 

slope  there  is  a 50-foot  drift  to  the  east, 
and  from  the  bottom  another  75  feet 
long  to  the  west.  Exposures  at  the 
mouth  of  the  slope  show  fine-grained 
sandstone  as  the  hanging  wall.  The 
nearest  diabase  is  that  of  the  main  mass, 
the  edge  of  which  lies  about  100  feet  to 
the  northeast. 

King  and  Jauss  mines. — The  King 
mine  is  situated  on  the  east  side  of 
Fishers  Run,  about  3,300  feet  north  of 
the  Price  mine  and  2,100  feet  northeast 
of  the  Bell  slope.  The  Jauss  shaft 
(fig.  17)  is  situated  near  the  east  bank 
of  the  creek,  750  feet  northwest  of  the 
King  workings.  The  shafts  of  these 
two  eastern  mines  were  located  by  dip- 
needle  indications.  They  were  started  in  diabase,  but  at  moderate 
depth  both  encountered  ore  associated  with  sedimentary  rocks.  The 
strata  dip  toward  the  north,  so  that  it  would  appear  that  they  must 
come  to  the  surface  south  of  the  shafts.  Nevertheless,  the  presence  of 
these  sediments  would  not  be  suspected  from  examination  of  the  sur- 


Fig.  17. — Survey  of  workings  at 
Jauss  mine,  near  Dillsburg,  made 
in  1888. 


° Frazer,  Persifor,  jr.,  Second  Geol.  Survey  Pennsylvania,  Rept.  CC,  1877,  p.  218. 


80 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


face,  because  their  outcrop  is  obscured  by  an  overwash  of  diabase  soil. 
Just  north  of  the  railroad  track,  however,  on  the  west  side  of  the  creek 
and  about  800  feet  from  the  Jauss  shaft,  a patch  of  sediments  may  be 
inferred  from  the  occurrence  of  sandstone  fragments  in  the  soil.  It 
seems  probable  that  these  two  masses  of  sedimentary  rock  may  be  con- 
nected, but  the  surface  is  covered  to  such  an  extent  that  nothing  posi- 
tive can  be  made  out.  It  is  entirely  possible  also  that  the  sediments 
of  the  western  patch  may  extend  farther  west  than  is  indicated  on 
the  map  (PI.  XX),  for  in  this  direction  there  is  a broad  swale  in 
which  the  presence  of  diabase  soil  may  be  misleading  as  to  the  actual 
extent  of  the  intrusive  rock.  The  trend  of  the  two  sedimentary  strips 
is  in  the  direction  of  the  Longnecker  shaft  on  the  west  and  toward 
an  embayment  in  the  outer  boundary  of  the  diabase  area  on  the  east. 
Along  this  general  line  the  main  mass  of  diabase  is  seen  to  be  partly 
divided  by  intercalated  sandstones  and  shales.  Whether  this  separa- 
tion becomes  more  or  less  extensive  in  depth  can  not  be  judged,  but 
from  the  fact  that  in  the  Longnecker  workings  the  bedded  rocks  ap- 


pear to  rise  to  a crest  beneath  the  diabase,  it  seems  possible  that  the 
dividing  masses  may  extend  farther  along  the  strike  underground 
than  is  apparent  from  surface  indications,  and  that  they  may  even 
connect  with  one  another. 

It  might  be  worth  while  to  explore  the  AA'estern  patch  of  sedimen- 
tary rocks  mentioned  above.  If  this  is  ever  done  it  may  be  assumed 
that  the  northern  contact  with  the  diabase  dips  toAA^ard  the  north,  as 
at  the  Jauss  mine.  On  this  basis  the  best  scheme  for  proving  the 
ground  would  be  to  sink  shafts  or  bore  holes  just  Avithin  the  diabase 
area  in  order  to  catch  the  contact  on  the  dip.  The  loAArer  contact  of 
the  bedded  rocks  might  also  be  explored  both  in  this  vicinity  and 
south  of  the  Jauss  mine.  A cross  section  showing  the  supposed  struc- 
tural relations  in  the  Adcinity  of  the  Jauss  mine  is  given  in  fig.  18.  It 
is  supposed  that  a section  through  the  Avestern  sedimentary  patch 
would  be  very  similar. 


YORK  COUNTY  DEPOSITS. 


81 


The  following  notes  concerning  the  King  mine  are  abstracted  from 
Frazer : ° 

The  shaft,  which  ivas  sunk  in  187G,  passes  through  23  feet  of  soil 
and  diabase,  beneath  which  there  was  9 feet  of  ore.  Toward  the  east 
a drift  20  feet  long  encountered  an  oblique  wall  of  diabase  on  the 
south  side.  Between  this  wTall  and  indurated  sandstones  on  the  north 
the  ore  formed  a wedge-shaped  mass.  From  the  end  of  this  20-foot 
drift  a slope  was  opened  upward  until  clay  was  encountered.  The 
course  of  this  slope  (X.  3°  E.)  and  its  angle  of  inclination  (22°)  give 
the  apparent  direction  and  amount  of  the  dip  of  the  ore  bed.  From 
the  bottom  of  the  slope  a drift  was  run  N.  5°  E.  for  a distance  of  50 
feet,  following  a fault  showing  slickensides.  Along  this  gangway  the 
fault  rock  is  a broken-up  mixture  of  sandstone  and  trap  rock.  About 
20  feet  east  of  the  slope  indurated  sandstone  exhibits  a dip  of  23° 
in  a direction  N.  40°  but  the  dip  of  the  vein  is  reported  to  be 
X.  10°  W. 

The  Jauss  shaft  is  situated  just  west  of  Fishers  Run,  at  the  eastern 
terminus  of  the  branch  railroad.  The  shaft  was  sunk  at  a point 
where  the  dip  needle  showed  a marked  magnetic  attraction.  About 
72  feet  of  diabase  was  penetrated  before  the  7- foot  ore  bed  was  en- 
countered. The  floor  of  the  mine  is  limestone  conglomerate.  As 
depth  was  gained  the  ore  bed  was  found  to  thicken  along  the  dip,  and 
in  the  lowTest  workings,  205  feet  below  the  surface,  a large  body  of  ore 
is  reported.  Stoping  was  carried  about  30  feet  above  the  point  where 
the  ore  was  cut  through  by  the  shaft.  A survey  made  in  1888  shows 
the  mine  workings  as  extending  270  feet  northwest  of  the  shaft.  In 
this  distance  the  ore  bed  falls  133  feet,  giving  an  average  inclination 
of  nearly  50  feet  per  100,  or  about  30°.  The  dip  appears  to  be  some- 
what steeper  in  the  lowrer  than  in  the  upper  workings. 

Material  on  the  waste  pile  shows  that  some  of  the  ore  at  least  has 
been  formed  by  replacement  of  limestone  conglomerate,  though  most 
of  the  material  intimately  associated  with  the  ore  is  a light-green  rock 
which  appears  to  be  an  altered  shale.  Although  no  fragments  of  any 
rock  except  diabase  are  to  be  seen  in  the  field  south  of  the  shaft,  there 
can  be  little  doubt  that  the  sedimentary  rocks  which  accompany  the 
ore  would  be  found  beneath  a relatively  shallow  cover  of  soil.  On  the 
geologic  map  ('PI.  XX)  a strip  of  sediments  is  indicated  as  extending 
southeast  to  the  King  mine. 

Altland  mine. — Just  where  the  switch  of  the  Bell  mine  joins  the 
main  track  there  are  three  shafts,  two  north  and  one  south  of  the  rail- 
road. These  constitute  the  Altland  mine,  concerning  which  the  notes 
in  the  following  paragraph  are  condensed  from  the  description  by 
D’lnvilliers : 6 

a Frazer,  Persifor,  jr.,  op.  cit.,  p.  212. 

b Ann.  Kept.  Geol.  Survey  Pennsylvania  for  1886,  pt.  4,  1887,  pp.  1506-1507. 

54370— Bull.  359—08 6 


82 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


This  mine  lies  northwest  of  the  Bell  mine  and  is  opened  by  a shaft 
62  feet  deep,  from  the  bottom  of  which  a slope  extends  northward 
on  the  ore  bed.  This  bed  evidently  lies  geologically  higher  than  the 
one  worked  at  Bell’s.  Its  outcrop  was  formerly  worked  a short  dis- 
tance south  of  the  shaft.  The  shaft  encountered  ore  at  57  feet  and 
the  slope  is  driven  northward  on  a 23°  dip  for  about  125  feet,  the 
ore  bed  ranging  from  4 to  7 feet  in  thickness.  All  along  the  slope 
the  hanging  wall  seems  to  be  a fine-grained  trap,  in  places  carrying 
small  crystals  of  iron  pyrites  and  here  and  there  nodules  of  lime. 
But  in  the  drifts  at  the  bottom  of  the  slope  for  25  feet  on  each  side 
an  indurated  slate  rock  wedges  in  between  the  trap  and  the  ore, 
forming  the  hanging  wail.  The  ore  body  seems  to  have  a lenticular 
shape,  as  at  the  Cox  mine,  being  thickest  at  the  slope  and  thinning 
rapidly  both  east  and  west.  The  upper  workings  are  confined  to  the 
vicinity  of  the  slope,  but  at  the  bottom  the  ore  bed  has  a workable 
thickness  for  a greater  distance  along  the  strike.  The  ore  is  rather 
micaceous. 

From  the  surface  distribution  of  the  diabase,  so  far  as  it  can  be 
made  out,  the  Altland  ore  seems  to  lie  some  distance  below  the  bottom 
of  the  main  diabase  mass.  It  is  possible  that  the  trap  mentioned  by 
D’Invilliers  is  a thin  eastward  extension  of  the  sill  shown  on  the 
geologic  map  (PL  XX)  as  ending  west  of  the  Longnecker  tract. 
If  this  is  the  case,  the  Altland  bed  and  the  ore  formerly  worked  at 
the  Smyser  pit  probably  correspond  in  stratigraphic  position,  and 
other  ore  shoots  may  exist  beneath.  Also,  if  the  Sn^ser  and  Altland 
beds  occupy  the  same  stratigraphic  horizon,  the  strike  of  the  strata 
is  diagonal  to  the  contact  of  the  main  diabase,  which  is  therefore 
slightly  crosscutting  in  this  vicinity,  just  as  it  is  farther  northwest, 
near  the  Underwood  workings.  From  this  conclusion  it  would  seem 
worth  while  to  seek  for  ore  along  the  strike  of  the  ore  bed  east  of 
the  Altland  mine.  At  the  contact  with  the  diabase  the  structural 
conditions  would  be  like  those  which  have  been  deduced  for  the  Bell 
deposit. 

Smyser  mine. — The  Smyser  open  pit  is  situated  about  450  feet 
west  of  the  Altland  workings,  and,  as  already  stated,  the  ore  bed 
probably  corresponds  in  position  with  that  in  the  Altland  mine. 
The  Smyser  deposit  was  opened  in  1852,  and  3,000  tons  of  ore  are 
reported  to  have  been  won  from  it.  Although  the  ore  is  said  to  have 
rested  upon  a saddle  of  diabase,  the  nearest  diabase  which  can  be 
determined  from  surface  observations  is  the  sill  which  passes  north 
of  the  pit.  This  sill  appears  to  end  a short  distance  west  of  the 
Longnecker  switch,  though  it  is  possible  that  it  may  extend  some- 
what farther  east. 

A small  body  of  ore  said  to  have  been  uncovered  in  the  railroad 
cut  just  west  of  the  road  crossing,  about  500  feet  distant  from  the 


YOKK  COUNTY  DEPOSITS. 


83 


Smyser  pit,  was  never  opened.  It  apparently  lies  in  lower  strata 
than  those  at  the  Smyser  pit. 

Bowlders  of  ore  may  be  found  in  the  cultivated  field  about  400 
feet  north-northeast  of  the  Smyser  pit  and  200  feet  north  of  the 
dwelling  house.  This  locality  is  apparently  inside  the  diabase  area, 
but  it  seems  possible  that  an  irregularity  in  the  bottom  of  the  diabase 
mass  has  brought  a small  patch  of  sediments  to  the  surface.  If  this 
supposition  is  correct,  the  occurrence  of  ore  at  this  place  is  favorable 
to  the  view  that  ore  deposits  will  be  found  in  many  places  beneath 
the  diabase  when  extensive  explorations  are  undertaken. 

Underwood  workings. — The  most  productive  ground  of  the  Dills- 
burg  field  has  been  the  northeasterly  35  acres  of  the  Underwood 
property  and  the  near-by  portions  of  the  McCormick  tract  on  the 
north  and  the  Logan  tract  on  the  east.  On  the  Underwood  tract 
there  are  five  large  open  pits  and  several  smaller  excavations,  all  of 
which  were  exhausted  previous  to  1874,  and  four  deep  mines,  which 
have  been  abandoned  since  1887. 

The  southernmost  of  the  Underwood  workings  are  two  pits  situ- 
ated about  500  feet  northwest  of  the  Smyser  pit,  on  opposite  sides 
of  the  north-south  wagon  road.  These  two  openings  are  doubtless 
on  the  same  ore  body,  which  they  have  developed  for  about  400  feet 
along  its  course.  Though  the  depth  of  the  workings  is  not  known, 
the  ore  must  have  been  followed  for  some  distance  on  a northerly 
dip,  because  there  are  depressions  about  175  feet  north  of  the  western 
opening  which  appear  to  be  the  result  of  the  caving  in  of  underground 
workings.  The  narrow  diabase  sill  which  passes  north  of  the  Smyser 
pit  touches  the  south  side  of  the  western  opening,  and  just  north  of 
the  pits  is  another  sill  which  strikes  northeast  and  west.  The  second 
sill  can  not  be  traced  east  of  the  wagon  road,  though  it  may  extend 
for  some  distance  in  this  direction.  The  two  sills  approach  each 
other  toward  the  west  and  finally  unite.  The  main  diabase  contact, 
running  from  southeast  to  northwest,  passes  near  the  northeast  cor- 
ner of  the  eastern  pit  and  the  strike  of  the  ore  bed  is  evidently  diag- 
onal to  this  contact  and  also  to  the  course  of  the  southern  sill,  but  it 
is  nearly  parallel  with  the  trend  of  the  northern  sill. 

The  next  openings,  to  the  northwest,  are  two  large  pits  in  which 
the  general  line  of  excavation  runs  from  the  outlying  sill  on  the  south- 
west diagonally  across  to  the  main  contact  on  the  northeast.-  The 
boundary  of  the  main  diabase  area  crosses  the  northeastern  of  the 
two  pits,  which  is  said  to  have  been  the  first  mine  opened  in  the  Dills- 
burg  field.  These  pits  must  have  furnished  a very  large  amount  of 
ore.  In  1873  a shaft  was  sunk  in  the  bottom  of  the  eastern  pit  (Der- 
rick shaft),  and  is  said  to  have  passed  through  25  feet  of  diabase  and 
28  feet  of  ore.  The  ore  body  is  known  to  have  been  worked  for  a 
distance  of  250  feet  northeast  of  the  shaft  and  it  probably  connects 


84 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


with  the  ore  worked  in  the  three  deep  mines  lying  immediately  to  the 
north.  Between  the  open  pits  and  the  Underwood  slope  the  ore  bed 
apparently  lies  very  flat.  Limestone  was  encountered  in  the  work- 
ings from  the  Derrick  shaft. 

About  GOO  feet  northwest  of  these  pits  there  is  another  large  pit, 
the  longer  axis  of  which  trends  northeastward,  nearly  parallel  with 
the  diabase  contact,  which  lies  about  50  feet  to  the  southeast.  Waste, 
apparently  derived  from  these  workings,  contains  limestone  and 
masses  of  garnet  rock.  A shaft  was  sunk  about  50  feet  beyond  the 
southwest  end  of  the  pit,  but  whether  or  not  ore  was  mined  from  this 
opening  is  not  known. 

Farther  north  there  are  two  large  pits  between  the  one  just  de- 
scribed and  the  McCormick  property  line.  In  both  of  thesQ  the 
strike  of  the  ore  bed  is  slightly  south  of  east.  Nothing  can  be  seen 
of  the  rocks  which  inclose  the  ore  and  it  is  not  known  to  what  depth 
the  deposit  was  excavated. 

Between  the  three  western  pits  of  the  Underwood  group  and  the 
edge  of  the  diabase  mass  many  small  ore  pockets  were  mined  out  at 
the  surface,  but  the  only  important  excavation  in  this  part  of  the 
tract  lies  in  the  angle  of  the  diabase  boundary,  about  300  feet  south 
of  the  big  McCormick  pit.  In  the  northeast  corner  of  this  excava- 
tion thin-bedded  layers  of  baked  sandstone  may  be  seen  dipping 
N.  80°  E.  at  an  angle  of  about  20°.  The  ore  evidently  passes  under 
this  sandstone,  which  therefore  lies  between  the  ore  and  the  diabase 
seen  on  the  east  side  of  the  pit. 

Of  the  three  deep  mines  on  the  Underwood  tract  which  remain 
to  be  described,  the  oldest  was  opened  by  the  so-called  Underwood 
slope,  the  position  of  which  is  shown  on  the  maps  (PI.  XX and  fig.  19) . 
The  following  notes  on  this  mine  are  condensed  from  Frazer’s 
report : ° 

The  slope  sinks  due  north  at  an  angle  of  28°.  Ore  was  not  fol- 
lowed from  the  surface,  but  was  reached  at  a depth  of  26  feet.  Dia- 
base is  exposed  at  the  mouth  of  the  slope,  and  the  ore,  where  first 
encountered,  is  said  to  have  been  18  feet  thick.  The  dip  of  the  ore 
beds  is  steeper  in  the  lower  workings  than  in  the  upper  part  of  the 
mine.  The  foot  wall  is  sandstone  intermixed  with  limestone;  the 
hanging  wall  is  diabase.  The  distance  between  the  walls  varies 
from  G to  30  feet.  Three  levels  have  been  opened.  On  the  first 
level,  at  120  feet,  drifts  extend  100  feet  east  and  west  of  the  slope. 
The  second  level,  at  180  feet,  was  opened  90  feet  east  and  west,  and 
the  third  level,  at  200  feet,  was  opened  110  feet  east  and  120  feet 
west.  The  ore  body  was  developed  by  raises  about  20  feet  apart, 
extending  from  level  to  level. 


° Second  Geol.  Survey  Pennsylvania,  Kept.  CC,  1877,  pp.  207-208, 


YORK  COUNTY  DEPOSITS. 


85 


Apparently  referring  to  this  same  slope,  D’Invilliers  states  in  his 
1886  report a that  the  workings  were  carried  down  500  feet  but  were 
abandoned.  He  also  says  that  the  slope  was  carried  down  with  the 
true  hanging  wall  (that  is,  diabase)  on  top;  but  within  a compara- 
tively short  distance  the  bed  forked  into  an  upper  and  a lower  seam, 
with  a wedge  of  slaty  sandstone  between.  The  gangways  driven  east  & 
from  the  slope  showed  the  ore*  being  rapidly  cut  out  by  the  con- 
vergence of  the  walls,  and  the  drifts  were  continually  kept  turning 
toward  the  northeast  in  order  to  keep  within  the  ore  body.  The 
best  ore  is  said  to  have  occurred  near  the  place  where  the  bed 


Fig.  19. — Plan  and  section  of  Underwood  and  Longnecker  mines,  Dillsburg,  showing 

probable  trend  of  ore  bed. 


pinched;  and  where  the  bed  is  thickest  the  ore  is  mixed  with  slaty 
limestone  layers  and  carries  iron  pyrites. 

In  April,  1887,  the  mine  was  worked  by  a shaft  96  feet  deep  which 
is  said  to  have  passed  through  three  ore  beds — the  first  at  38  feet, 
7 to  8 feet  thick  and  rather  lean ; then  14  feet  of  sandstone ; 8 feet 
of  good  ore;  26  feet  of  sandstone;  and  the  bottom  ore  bed,  15  to  20 
feet  thick.  These  extensive  workings  lie  entirely  east  of  the  old 
slope.  As  in  the  other  mines,  the  foot  wall  is  a hard  white  cal- 
careous sandstone,  and  the  hanging  wall  is  diabase ; but  between  the 

“ Ann.  Rept.  Geol.  Survey  Pennsylvania  for  1886,  pt.  4,  1887,  p.  1508. 

b This  word  is  west  in  the  original,  but  the  concurrence  of  the  words  “ west  ” and 
“ northwest  ” in  this  sentence  makes  it  unintelligible  as  it  stands. 


86  MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 

Avails  lenticular  masses  of  sandstone  and  slate  wedge  into  the  ore 
body.  It  is  no  doubt  due  to  the  swelling  of  such  wedges  that  the 
three  beds  of  ore  were  found  in  the  shaft.  The  middle  bed,  Avhich 
has  been  somewhat  largely  developed,  is  said  to  lie  between  beds 
of  altered  sand  rock.  In  the  lowest  bed  immense  chambers  have 
been  opened  where  the  ore  swells  locally;  but  where  the  bed  is  15 
to  20  feet  thick  it  contains  seams  of  limestone  and  bowlders  of  barren 
rock.  The  two  upper  beds  are  regarded  as  splits  from  the  lowest  or 
main  bed.  The  mine  may  have  furnished  from  20,000  to  25,000  tons 
of  ore,  averaging  40  per  cent  of  iron. 

The  last  mine  opened  on  the  Underwood  tract  is  described  by 
D’Invilliers  ° under  the  heading  “ Longnecker  mine,”  a name  now  ap- 
plied to  the  mine  on  the  Logan  tract.  The  writer  was  not  able  to 
determine  the  location  of  this  opening,  which  is  said  to  lie  a little 
east  of  the  Underwood  mine. 

According  to  D’lnvilliers,  the  shaft  is  95  feet  deep  and  the  slope 
extending  from  its  bottom  has  reached  the  McCormick  line  and  is 
probably  from  400  to  450  feet  long.  On  the  east  four  gangways 
have  been  driven  toward  the  Longnecker  mine,  and  from  the  bottom 
of  the  slope  a gangway  has  been  driven  150  feet  west  toward  the 
Underwood  mine.  About  50  feet  from  the  slope,  in  a stope  above  the 
west  gangway,  the  ore  in  places  is  20  to  30  feet  thick.  No  new 
features  are  presented  in  this  mine,  and  it  may  be  considered  that  the 
ore  is  an  extension  400  feet  farther  to  the  east  of  the  Underwood 
bed.  It  may  be,  however,  that  there  are  two  ore  lenses  Avhich  overlap 
each  other. 

The  apparent  relations  of  the  ore  and  the  diabase,  so  far  as  they 
may  be  judged  from  the  recorded  descriptions  of  the  Underwood 
slope,  are  illustrated  in  the  cross  section  (fig.  19). 

The  position  of  the  section  is  90  feet  east  of  the  Underwood  slope 
and  its  direction  is  north  and  south. 

Longnecker  mine. — The  mine  now  known  as  the  Longnecker  was 
formerly  called  the  Logan  mine.  It  was  opened  by  the  owner  of 
the  property,  J.  N.  Logan,  in  1874.  The  shaft  was  located  from 
dip-needle  indications,  but  27  feet  of  diabase  was  penetrated  before 
the  ore  was  cut.  Diabase  soil  and  bowlders  cover  the  surface  near 
the  mine,  and  it  is  evident  that  the  ore  must  lie  beneath  the  mass  of 
this  rock.  Material  on  the  mine  dump  shows  that  limestone  con- 
glomerate is  present  in  the  workings. 

The  ore  bed  is  said  to  have  been  20  feet  thick  at  the  shaft  and  to 
have  averaged  10  feet  in  the  mine.  From  the  bottom  of  the  vertical 
shaft,  51  feet  deep,  a slope  toward  the  north  starts  at  an  inclination 
of  28°,  but  flattens  somewhat  as  depth  is  attained.  Mr.  Logan 


a Op.  cit.,  pp.  1509-1510. 


YORK  COUNTY  DEPOSITS. 


87 


states  that  the  workings  extend  about  300  feet  north  of  this  shaft 
and  that  the  east  drift  of  the  lowest  level  is  190  feet  long.  The  ex- 
tent of  the  workings  in  1885  is  shown  by  the  plan  (fig.  20).  Con- 
siderable work  has  been  done  since  this  survey  was  made.  The 
vertical  section  which  accompanies  the  plan  does  not  correspond 
with  the  relations  as  they  are  stated  above,  but  it  is  reproduced  as 


Fig.  20. — Plan  and  cross  section  of  Longnecker  mine,  on  Logan 
tract,  Dillsburg.  From  Ann.  Rept.  Second  Geol.  Survey 
Pennsylvania  for  1885,  p.  568. 


originally  drawn.  From  the  inclination  of  the  slope  the  ore  bed 
should  outcrop  about  50  feet  south  of  the  shaft,  but  at  this  place 
the  surface  rock  is  undoubtedly  diabase.  The  map  shows  that  the 
underground  workings  reach  a point  fully  100  feet  south  of  the 
shaft,  so  that  the  under  side  of  the  diabase  must  lie  nearly  flat  south 
and  southwest  of  the  shaft,  as  it  does  in  the  ground  south  and  south- 
east of  the  Underwood  slope.  In  the  vicinity  of  the  shaft  the  bottom 


88 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


of  the  diabase  takes  an  abrupt  dip  toward  the  north,  as  in  the  Un- 
derwood mine,  so  that  both  the  Longnecker  shaft  and  the  Under- 
wood slope  appear  to  have  penetrated  the  ore  bed  just  at  the  angle 
where  the  steeper  dip  begins. 

The  very  considerable  extent  of  the  ore  bed  shown  by  the  Under- 
wood and  Longnecker  workings  furnishes  a strong  reason  for  be- 
lieving that  the  Logan  tract  offers  good  ground  for  further  develop- 
ment. The  Underwood  tract  seems  to  have  been  completely  worked 
out,  though  from  the  statement  that  the  Longnecker  workings  ex- 
tended north  to  the  McCormick  line  it  seems  possible  that  the  same 
bed  of  ore  continues  into  the  McCormick  tract.  A consideration  of 
all  the  deep  mines  of  this  vicinity,  however,  suggests  that  the  actual 
trend  of  the  ore  is  toward  the  northeast,  so  that  future  discoveries 
are  more  likely  to  be  made  in  the  Logan  tract  than  elsewhere.  The 
boring  which  was  made  in  the  McCormick  pit  appears  to  be  not 
deep  enough  to  reach  the  extension  of  the  Underwood  ore.  It  is 
reported  that  a boring  was  made  about  1,500  feet  north  of  the 
Longnecker  shaft,  but  no  record  of  this  work  is  available. 

McCormick  mines. — On  the  McCormick  tract,  situated  north  of  the 
Underwood  tract,  there  are  three  large  pits  and  several  small  open- 
ings, all  of  Which  Avere  abandoned  before  1875.  No  large  masses  of 
diabase  are  present  near  most  of  the  excavations,  but  the  largest  pit 
is  situated  at  the  Avestern  edge  of  the  main  diabase,  about  200  feet 
north  of  the  pit  in  the  angle  of  the  diabase  boundary  on  the  Under- 
Avood  tract.  This  large  pit  is  said  to  have  been  opened  about  1850, 
and  it  is  apparent  from  the  fact  that  its  area  is  nearly  12,000  square 
feet  that  it  must  have  furnished  a large  amount  of  ore.  The  size  of 
the  vein  is  not  recorded,  but  the  longer  axis  of  the  excavation  trends 
somewhat  north  of  east,  showing  -that  the  strike  of  the  ore  bed  is  in 
that  direction.  The  position  of  the  slope  by  which  the  mine  aauis 
worked  indicates  that  the  strata  have  the  usual  dip  toAvard  the  north. 

Frazer  states  ° that  a shaft  was  sunk  from  the  bottom  of  the  pit  to 
a depth  of  140  feet,  and  that  about  100  feet  north  of  the  pit  a 20-foot, 
slope  AA^as  put  doAvn  60  feet  on  the  vein  of  ore,  which  AATas  4 feet  thick 
at  the  bottom.  He  gives  the  following  record  of  a drill  hole  in  the 
large  pit : b 

Record  of  bore  hole  No.  5 , sunk  in  McCormick  & Co.'s  old  bank. 


Feet. 

Soil 8.  84 

Green  sandstone • 17 

Iron  ore • 17 

Gray  sandstone 4-  50 


White  sandstone 

Reddisli-green  sandstone 


Second  Geol.  Survey  Pennsylvania,  Kept.  CC,  1877,  p.  214. 


6 Op.  cit.,  p.  216. 


YORK  COUNTY  DEPOSITS. 


89 


Black  (?)  trap 

Gray  sandstone 

Iron  ore 

White  sandstone 

Iron  ore 

White  sandstone 

Limestone  and  flint 

Limestone  and  fire  clay. 

Bed  sandstone 

Green  sandstone 

White  sandstone 

Green  sandstone 

Iron  ore 

Sandstone 

Sandstone  and  ore 

Limestone  and  flint 

Ore  and  sandstone 

Green  sandstone 

White  sandstone 

Green  sandstone 

White  sandstone 

Gray  trap 

White  sandstone 

Limestone 

Gray  sandstone 

Bed  sandstone 

White  sandstone 

Bed  sandstone 

White  sandstone 

Bed  sandstone 

White  sandstone 


Feet. 
23.  07 
3.  25 

3.  25 

5.00 

1.  33 
11.  00 

6.  00 
10.  00 
14.00 

4.  00 
9.  00 

3.00 

2.  00 
2.  00 
3.  00 
6.50 

.50 

5.00 

5.  00 

6.  00 
1.  00 
2.  00 
2.  00 

3.  00 

4.  50 

4.00 
4.  00 
1.  00 
4.  00 

3.  00 

4.  50 


187.  83 

It  is  evident  from  the  above  record  that  the  mass  of  diabase  which 
outcrops  east  of  the  pit  does  not  dip  beneath  this  ore  body.  The  con- 
tact of  the  diabase  with  the  stratified  rocks  might  be  supposed  to  be 
highly  inclined  and  strongly  crosscutting,  except  for  the  fact  that 
about  400  feet  toward  the  southeast,  at  the  bottom  of  the  Longnecker 
slope,  the  lower  surface  of  the  diabase  is  not  more  than  200  feet  deep. 
It  seems  probable,  therefore,  that  this  lower  surface  dips  rather 
gently  toward  the  east  or  northeast.  The  most  likely  situation  for 
a continuation  of  the  ore  body  would  be  where  the  northward-dipping 
strata  meet  the  eastward  or  northeastward  dipping  bottom  of  the 
diabase. 

Though  the  drill-hole  record  shows  thin  layers  of  ore  at  five  hori- 
zons and  limestone  at  three  horizons,  it  is  not  likely  that  strata  equiva- 
lent to  those  containing  the  ore  in  the  Underwood  deep  mines  have 
been  reached.  If  these  beds  continue  with  the  same  dip  that  they 
have  in  the  Underwood  slope,  their  position  would  be  about  450  feet 
from  the  surface  beneath  the  McCormick  pit. 


90 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


The  second  McCormick  pit  is  a long,  narrow  excavation  situated 
just  north  of  the  property  line,  about  200  feet  farther  west.  (See 
fig.  21.)  Nothing  is  known  of  this  ore  layer  beyond  the  fact  that  it 
strikes  slightly  north  of  west.  The  pit  is  about  50  feet  north  of  the 
nearest  Underwood  pit. 

The  McCormick  long  cut  lies  about  300  feet  northwest  of  the  large 
pit  and  230  feet  north  of  the  excavation  last  mentioned.  Though 
there  are  some  small  openings  beyond,  the  long  cut  is  the  northern- 
most of  the  formerly  productive  mines  of  the  Dillsburg  field.  The 
ore  bed  was  opened  for  a distance  of  325  feet  along  the  strike  and 


Fig.  21. — Sketch  map  showing  situation  of  pits  and  test  holes  on 
McCormick  tract,  Dillsburg. 


small  openings  were  made  at  several  places  west  of  the  main  cut. 
The  following  notes  are  taken  substantially  from  Frazer:® 

A dolerite,  which  occurs  in  this  mine  at-  the  surface  and  appears 
to  constitute  the  top  rock  of  the  ore,  dips  N.  5°  W.  from  27°  to  34°. 
Two  slopes  were  driven  to  find  the  ore.  The  upper  one  followed 
the  vein  in  between  well-defined  walls  at  a normal  angle  to  the  incli- 
nation of  the  sandstone  layers.  The  upper  sandstone  was  continued 
in  the  deep,  but  the  foot  wall  was  cut  out  by  a dike  of  diabase.  The 
lower  slope,  of  about  30°  to  45°,  was  continued  for  180  feet  and  passed 
through  the  ore,  which  appeared  to  be  a very  irregular  deposit.  In 
1875  it  wras  nearly  exhausted. 


a Second  Geol.  Survey  Pennsylvania,  Kept.  CC,  1877,  p.  215. 


YORK  COUNTY  DEPOSITS. 


91 


Near  the  west  end  of  the  cut,  fine-grained  baked  sandstone  may  be 
seen  to  form  the  hanging  wall,  but  no  evidence  was  found  on  the  sur- 
face that  diabase  is  present  near  the  mine.  The  sketch  map  (fig.  21) 
shows  the  position  of  the  several  bore  holes,  the  records  of  which, 
here  given,  are  taken  from  Frazer:® 

Record  of  bore  hole  No.  1,  north  of  McCormick  long  cut. 


Feet 

Clay 4 

Sandstone  8 

Clay 2 

Bastard  limestone 9.  5 

Sandstone 9.  5 

Trap 9 

Unknown,  about 20 

Brown  sandstone 12 

Iron  ore 0 

Sandstone T 4 

Lean  iron  ore 4 


88 


Record  of  bore  hole  No.  3,  north  of  McCormick  long  cut. 


Feet. 

Clay 4 

White  sandstone 6 

Red  sandstone 7 

Trap 17.  5 

Black  and  green  sandstone 4 

Brown  sandstone 1 

Green  sandstone 8 

White  sandstone 1.  5 


49 


Record  of  bore  hole  No.  If,  southeast  of  McCormick  long  cut. 


Feet. 

Clay 2 

Gray  sandstone 8 

Red  sandstone 7 

Unknown 10 

White  sandstone 7.  5 

Greenish-white  sandstone 6. 16 

White  sandstone 6.  41 

Green  sandstone 2.  83 

Red  sandstone . 50 

Black  (?)  trap 16.08 

White  (?)  trap 6.66 

Ore 1.  50 

White  sandstone 22.  25 

Green  sandstone ^ 13. 16 

Red  and  white  sandstone 6.  00 


116.  04 


Op.  cit.,  pp.  215-216. 


92 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Hole  No.  1,  located  about  110  feet  north  of  the  long  cut,  evidently 
penetrated  the  ore  bed,  which  was  mined  from  the  surface.  The  rec- 
ord of  hole  No.  2 is  not  given.  To  judge  from  the  known  dip  of  the 
strata,  hole  No.  3,  about  50  feet  north  of  the  cut,  must  also  have  passed 
through  the  horizon  where  the  ore  body  should  be,  though  no  ore  was 
reported.  The  9^-foot  bed  of  limestone  encountered  in  hole  No.  1 
probably  outcrops  north  of  hole  No.  3.  The  record  of  hole  No.  5 is 
given  on  pages  88-89. 

The  position  of  two  small  pockets  of  ore  about  200  feet  north  of 
the  east  end  of  the  long  cut  is  indicated  on  the  map  (PI.  XX).  A 
small  quantity  of  ore  is  said  to  have  been  mined  from  a shaft  1,200 
feet  northeast  of  the  long  cut  in  the  northeast  angle  of  the  crossroads. 

The  position  of  this  shaft  is  very  near  the  boundary  of  the  main 
mass  of  diabase. 

Mr.  Logan  states  that  thin  seams  of  magnetite,  or  of  specular 
hematite,  have  been  found  at  several  points  in  the  fields  of  his  home 
farm,  about  half  a mile  northwest  of  the  McCormick  long  cut.  In 
this  vicinity  there  are  several  minor  bodies  of  diabase,  but  the  shales 
and  sandstones  are  not  generally  baked,  as  they  are  in  the  neighbor- 
hood of  the  old  mines. 

DIABASE  INTRUSIONS  WEST  OF  THE  MINES. 

The  present  examination  of  the  geologic  features  of  the  Dillsburg 
field  has  revealed  the  presence  of  several  bodies  of  diabase  on  the 
western  slope  of  the  hill  on  which  most  of  the  old  mines  are  situated. 
The  intrusions,  which  are  four  in  number,  appear  at  the  surface  as 
narrow  bands,  and  though  the  relation  which  they  bear  to  the  inclos- 
ing rocks  can  not  be  observed,  they  are  probably  sills,  more  or  less 
closely  conforming  with  the  bedding  of  the  rocks  which  incase  them. 
One  of  the  bands  is  the  westward  and  northwestward  extension  of  the 
two  narrow  strips  of  diabase  which  cross  the  wagon  road  just  south 
of  the  Underwood  pits  and  come  together  about  500  feet  west  of  the 
road.  Where  the  two  forks  merge  the  band  is  250  feet  wide,  though 
it  becomes  narrower  toward  the  west.  Its  observed  length  is  about 
2,500  feet,  but  its  western  termination  is  not  seen  because  of  the  deep 
soil  in  the  meadows  between  the  ore  fields  and  Dillsburg.  The  three 
northern  bands  extend  eastward  nearly  to  the  brow  of  the  hill.  The 
middle  band  runs  northwestward  for  800  or  900  feet,  to  a point  where 
it  appears  to  terminate,  though  this  is  not  certain,  for  the  surface 
debris  in  this  vicinity  is  greatly  mixed.  The  other  bands  may  be 
traced  toward  the  northwest  until  they  are  lost  under  the  meadow 
soil.  The  northernmost  band  may  be  followed  nearly  to  the  wagon 
road,  as  shown  on  the  map  (PI.  XX). 

On  page  94  reasons  are  given  in  support  of  the  suggestion  that  beds 
of  limestone  conglomerate  which  occur  in  the  vicinity  of  Dillsburg 


YORK  COUNTY  DEPOSITS. 


93 


may  extend  eastward  and  underlie  the  meadows  between  the  town  and 
mines.  If  any  such  continuity  of  conglomerate  layers  actually  ex- 
ists, they  must  traverse  the  ground  occupied  by  the  four  diabase  sills. 
From  what  has  been  learned  concerning  the  geology  of  the  Dillsburg 
deposits,  it  seems  that  the  possibility  of  beds  of  limestone  conglom- 
erate being  locally  in  contact  with  these  intrusions  makes  all  of  this 
ground  worthy  of  careful  exploration.  The  absence  of  ore  indica- 
tions in  the  soil  can  not  be  considered  conclusive  evidence  against  the 
existence  of  ore  bodies,  as  the  ore  is  known  to  break  down  completely 
under  long-continued  action  of  the  weather,  and  as  on  the  hill  slope 
the  earthy  material  resulting  from  the  superficial  disintegration  of 
an  ore  body  would  be  hidden  more  completely  than  on  nearly  level 
ground  because  of  the  gradual  downhill  movement  of  the  rock  frag- 
ments and  soil. 

PRACTICAL  CONCLUSIONS. 

A practical  question  to  which  an  unqualified  answer  can  not  be 
given  is  whether  or  not  deposits  of  magnetic  iron  ore  may  yet  be 
found  in  new  localities  in  the  Dillsburg  district.  It  seems  unlikely 
that  new  ore  bodies  will  be  discovered  from  surface  showings  encoun- 
tered  in  tilling  the  soil,  as  in  the  earlier  days  of  the  district.  Four 
of  the  ore  bodies  have  been  discovered  by  means  of  the  magnetic  dip- 
ping needle,  and  others  may  yet  be  found  in  the  same  way.  In  this 
connection,  though  no  magnetic  observations  were  made  during  the 
present  investigation,  it  may  be  pointed  out  that  in  using  the  mag- 
netic needle  difficulties  may  arise  from  the  attraction  due  to  masses 
of  diabase,  for  it  is  well  known  that  this  rock  possesses  magnetic 
properties  in  certain  places.  On  the  other  hand,  it  seems  possible 
that  there  may  be  ore  bodies  which  the  needle  will  not  detect. 

Whatever  may  be  the  truth  on  the  foregoing  points,  their  considera- 
tion is  secondary  to  the  understanding  of  the  geologic  features  of  the 
district,  the  presentation  of  which  is  the  object  of  this  report.  From 
a purely  geologic  standpoint,  deposits  of  ore  like  those  which  have 
already  been  worked  might  be  expected  to  occur  west  of  the  ore  fields 
along  the  borders  of  the  several  diabase  intrusions  near  Dillsburg. 
The  particular  feature  which  distinguishes  this  part  of  the  district 
and  makes  it  seem  more  likely  that  ore  deposits  may  be  present  here 
than  at  other  places  in  York  County  where  large  masses  of  diabase 
occur  is  the  existence  of  beds  of  limestone  conglomerate.  This  rock 
is  so  closely  associated  with  the  ore  bodies  of  the  mines  already 
worked  that  its  presence  must  be  regarded  as  one  of  the  favorable 
conditions  for  ore  occurrence,  and  where  it  comes  into  contact  with 
diabase  the  chances  for  finding  ore  seem  worthy  of  attention. 

The  mile- wide  band  of  diabase  which  runs  east  and  west  just 
south  of.  the  ore  fields  narrows  somewhat  and  assumes  a northwest- 


94 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


erly  trend  about  1 mile  southeast  of  Dillsburg.  The  southern  part 
of  the  town  is  underlain  by  the  mass  of  intrusive  rock,  but  here  the 
band  makes  another  turn,  this  time  sharply  toward  the  southwest, 
and  it  continues  in  this  general  direction  for  about  8 miles  to  its  ter- 
mination a mile  or  more  northwest  of  York  Springs.  Southwest 
of  Dillsburg  minor  indications  of  ore  have  been  found  at  several 
points  along  the  borders  of  this  intrusion,  and  at  two  places  small 
bodies  of  ore  have  been  mined,  as  already  noted.  It  is  not  possible 
to  show  the  presence  of  limestone  conglomerate  at  any  of  these 
places,  though  outcrops  at  several  points  show  that  beds  of  the  rock 
are  present  beneath  the  low  meadows  between  Dillsburg  and  Beaver- 
town.  There  can  be  little  doubt  that  the  limestone  conglomerate  and 
diabase  actually  come  together  in  several  places,  though  the  contact 
may  lie  some  distance  beneath  the  surface. 

On  the  geologic  map  (PI.  XIX)  the  position  of  known  outcrops  of 
limestone  conglomerate  has  been  shown.  At  the  quarry  beside  the 
Dillsburg- York  Springs  road,  1 mile  southwest  of  Dillsburg,  a heavy 
bed  of  the  conglomerate  dips  toward  the  southeast,  so  that  if  the  dia- 
base, which  lies  east  of  the  road,  is  a crosscutting  mass,  as  seems  likely, 
the  stratum  should  come  into  contact  with  the  igneous  rock  in  this 
direction.  Though  baking  of  the  sediments  does  not  extend  as  far 
as  the  quarry,  the  presence  of  ore  at  the  surface  one- fourth  mile  to 
the  south  shows  that  solutions  capable  of  depositing  iron  were  active, 
and  the  chances  that  the  conglomerate  bed  is  mineralized  at  the  con- 
tact seem  worthy  of  consideration. 

One  mile  southwest  of  the  quarry  mentioned  in  the  foregoing 
paragraph,  limestone  conglomerate  has  been  exposed  at  the  eastern 
base  of  the  diabase  hill  along  an  abandoned  railroad  grade.  Here 
a considerable  degree  of  metamorphism  is  shown  by  the  presence  of 
silicate  minerals  in  the  conglomerate,  but  no  iron  minerals  have  been 
introduced.  The  absence  of  ore  in  this  place  is  possibly  to  be  charged 
to  the  small  size  of  the  diabase  intrusion  lying  immediately  west. 

It  is  impossible  to  discover  the  attitude  of  the  strata  between  the 
outlying  body  of  diabase  just  mentioned  and  the  long  dike  which 
extends  southwest  of  Dillsburg,  but  the  rocks  are  much  baked  as  the 
edge  of  the  dike  is  approached,  and  beds  of  limestone  conglomerate 
are  likely  to  exist  beneath  the  surface  debris.  In  the  event  of  a suc- 
cessful outcome  of  future  explorations  in  other  localities,  it  may  yet 
be  thought  desirable  to  determine  whether  or  not  limestone  conglom- 
erate occurs  in  the  vicinity  of  this  southwest  dike,  and  if  it  is  found, 
to  explore  those  places  where  it  is  likely  to  come  into  contact  with  the 
diabase.  The  existence  of  ore  at  the  Bender  mine  and  of  ore  indica- 
tions about  half  a mile  southeast  of  that  opening  shows  at  least  that 
mineralizing  waters  were  active  in  the  neighborhood. 


YOEK  COUNTY  DEPOSITS. 


95 


The  dike  or  sill  of  diabase  which  crosses  Dogwood  Run  northwest 
of  Dillsburg  has  been  traced  in  a northwesterly  direction  and 
found  to  connect  with  the  wide  intrusion  south  of  the  Grantham 
mines.  Exposures  of  limestone  very  near  the  diabase  are  seen  in  the 
wagon  road  near  the  gristmill,  in  a railroad  cutting  near  the  upper 
end  of  the  mill  pond,  and  along  the  creek  above  the  pond. 

The  attitude  of  the  main  diabase  mass  can  not  be  made  out,  but 
in  the  railroad  cutting  it  is  evident  that  the  limestone  is  cut  across  by 
several  irregular  intrusions  of  the ' igneous  rock.  The  limestone 
where  seen  is  not  greatly  metamorphosed,  though  the  lack  of  red 
color  in  the  soil  indicates  that  the  associated  shales  and  sandstones 
are  considerably  altered.  The  diabase  mass  forms  a prominent  hill 
lying  north  and  west  of  the  creek,  and  from  the  contour  of  this  hill 
it  is  judged  that  the  intrusion  does  not  form  the  floor  of  the  broad 
valley  east  of  Beavertown.  In  the  area  between  the  diabase  hill  and 
South  Mountain  there  are  no  rock  exposures,  except  in  the  quarry 
above  Beavertown.  This  opening  has  been  made  about  a sink,  and 
50  feet  of  limestone  conglomerate  has  been  exposed.  Other  sink  holes, 
extending  in  a northeast  direction,  suggest  that  the  same  stratum 
continues  for  fully  a mile  in  a northeasterly  direction  along  the  edge 
of  the  Mesozoic  belt.  Beds  of  conglomerate  may  come  into  contact 
with  the  diabase  beneath  the  deep  mantle  of  soil  on  the  west  and 
northwest  slopes  of  the  hill,  so  that  this  ground  may  be  worth  pros- 
pecting. 

In  the  neighborhood  of  Dillsburg  the  body  of  diabase  which  has 
been  under  consideration  lies  well  within  the  Mesozoic  area,  but  2 
miles  north  of  town  it  lies  between  Mesozoic  strata  on  the  southeast 
and  Paleozoic  limestone  on  the  northwest.  In  a limestone  quarry 
one-half  mile  south-southeast  of  the  D.  and  M.  J unction  the  limestone 
and  diabase  are  seen  almost  in  contact.  The  fact  that  the  limestone 
shows  no  evidence  of  having  been  affected  in  any  way  by  the  diabase 
suggests  that  in  this  place  the  two  rocks  have  been  brought  together 
by  a fault.  Though  this  structure  can  not  be  proved  from  the  features 
to  be  seen  in  this  quarry,  there  are  strong  reasons  for  believing  that 
the  boundary  between  the  Mesozoic  area  and  the  older  rocks  of  the 
valley  and  of  South  Mountain  is  formed  by  a profound  fault  for  at 
least  25  miles  southwest  of  the  Susquehanna  and  for  some  distance 
east  of  that  river.  The  probability  that  this  fault  exists  and  that 
movements  have  taken  place  along  it  since  the  intrusion  of  the  diabase 
removes  the  contact  with  the  Paleozoic  limestones  from  consideration 
as  a place  in  which  ore  bodies  are  to  be  expected. 

Inasmuch  as  it  is  wholly  impossible  to  estimate  the  thickness  of 
the  Mesozoic  strata  in  the  vicinity  of  Dillsburg  or  to  judge  either  the 
distribution  of  the  rocks  which  lie  below  these  beds  or  the  subter- 


96 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


ranean  forms  and  courses  of  the  intrusive  mass  of  the  diabase,  no  sug- 
gestions can  be  made  concerning  the  possibility  of  ore  deposits  being 
present  beneath  the  Mesozoic  formations. 

GRANTHAM  MINES. 

On  the  south  side  of  Yellow  Breeches  Creek,  near  Grantham  cross- 
ing, are  situated  three  old  mines,  known  as  the  Landis  or  Fuller,  the 
Porter,  and  the  Shelley.  Outcrops  in  the  railroad  cuts  and  material 
on  the  mine  dumps  show  that  the  deposits  at  this  place  occur  in 
Mesozoic  strata,  which  include  beds  of  limestone  conglomerate. 
North  of  Yellow  Breeches  Creek  the  bed  rock  is  Paleozoic  limestone, 
and  just  south  of  the  mines  diabase  appears.  This  diabase  is  part 
of  an  intrusive  mass  of  important  size,  extending  westward  and 
southwestward  to  the  vicinity  of  Dillsburg  and  eastward  for  4 miles 
or  more  to  join  a great  mass  of  the  same  rock  which  forms  the  group 
of  high  hills  between  Dillsburg  and  Mount  Airy.  Just  south  of 
Grantham  the  intrusion  is  about  1 mile  wide.  Eastward  from  Rose- 
garden,  its  northern  boundary  is  an  irregular,  waving  line,  which  has 
not  been  traced  in  detail  beyond  Grantham.  Near  the  mines  the 
strata  adjacent  to  the  diabase  are  undoubtedly  considerably  dis- 
turbed, as  is  indicated  by  varying  dips  in  the  old  workings.  It 
seems,  however,  that  the  average  ore-bearing  beds  decline  gently 
toward  the  south  and  pass  beneath  the  diabase,  so  that  the  latter 
forms  a general  hanging  wall  over  the  deposits.  The  Landis  and 
Porter  openings  are  situated  just  at  the  edge  of  the  diabase,  and  at 
the  Shelley  mine  a shaft  is  said  to  have  penetrated  diabase  lying 
just  above  the  ore.  One  mile  up  the  railroad  track  from  Grantham, 
at  Rosegarden,  diabase  is  seen  along  the  tracks,  and  one-third  mile 
farther  west  Paleozoic  limestone  appears  only  a short  distance  be- 
yond the  last  outcrop  of  the  igneous  rock.  Here,  then,  the  diabase 
comes  into  contact  with  the  older  rocks.  In  the  field  south  of  the 
railroad  debris  revealed  by  gullies  cut  into  the  hill  slopes  shows  the 
presence  of  sandstone  beneath  the  diabase.  These  sandy  beds  can 
continue  toward  the  west  for  a short  distance  only,  for  undoubted 
Paleozoic  limestone  is  again  observed  very  near  the  diabase  on  the 
highway  just  south  of  the  crossroads.  In  the  valley  of  the  small 
brook  which  joins  the  creek  at  Rosegarden  is  an  old  prospecting- 
shaft,  situated  at  the  south  edge  of  the  diabase  mass.  No  indications 
of  ore  are  to  be  seen  in  the  material  on  the  dump,  but  the  amount 
of  material  thrown  out  indicates  that  considerable  work  was  done 
at  this  place.  The  rock  excavated  is  mainly  a hard  baked  shale. 

Northeast  of  Grantham,  on  the  north  side  of  the  creek,  is  a mass  of 
diabase  which  may  have  been  separated  from  the  main  mass  by  the 
erosion  of  the  creek  channel.  On  the  south  side  of  this  mass,  in  the 
wooded  ravine  about  one-half  mile  east  of  the  railroad,  there  is  an  old 


YOEK  COUNTY  DEPOSITS. 


97 


prospect  pit  in  which  baked  sandstone  occurs.  Along  the  railroad 
track  the.  diabase  is  to  be  seen  in  contact  with  Paleozoic  limestone, 
blit  as  the  latter  is  not  notably  metamorphosed  at  this  place  it  is 
thought  that  the  contact  is  not  an  intrusive  one,  but  that  a fault  has 
brought  these  two  rocks  together.  This  suggestion  brings  up  the 
general  structural  problem  presented  by  the  northerly  boundary  of 
the  Mesozoic  belt  throughout  the  State,  discussion  of  which  will 
not  be  attempted  here. 

In  the  fact  that  they  occur  between  beds  of  limestone  conglomerate 
and  overlying  diabase  the  ore  deposits  near  Grantham  resemble  sev- 
eral of  the  deposits  of  the  Dillsburg  group,  the  same  relation  being 
observed  in  the  Underwood,  Longnecker,  Jauss,  Price,  and  Logan 
workings. 

In  the  absence  of  any  adequate  data  concerning  the  amount  of  iron 
ore  that  has  been  extracted  from  these  mines  and  the  degree  of  per- 
sistence shown  by  the  ore  bodies  in  the  ground  opened,  it  is  difficult 
to  judge  whether  prospecting  in  the  vicinity  for  other  deposits  would 
be  advisable  or  not.  From  a purely  geologic  standpoint  conditions 
similar  to  those  existing  near  the  known  ore  bodies  may  be  supposed 
to  extend  for  a considerable  distance  both  east  and  west  of  the  old 
openings.  The  place  to  look  for  ore  is  evidently  just  beneath  the 
diabase,  and  where  conglomerate  is  present  under  the  igneous  rock 
ore  is  likely  to  be  found.  The  most  feasible  way  to  make  a test  is  by 
a line  of  drill  holes  located  just  within  the  boundary  of  the  diabase 
area.  Perhaps  the  most  attractive  scheme  of  prospecting  would  be 
to  determine  by  means  of  the  drill  whether  or  not  the  deposits  already 
known  extend  beyond  the  old  workings  in  the  direction  of  the  dip. 

The  following  data  concerning  the  three  old  mines  at  Grantham 
are  condensed  from  F razer’s  report : a 

The  Landis  mine  was  opened  about  1863.  A tunnel  from  the  rail- 
road and  close  to  the  banks  of  the  creek  enters  a steep  bank  due 
south  for  200  feet.  Two  drifts  lead  off  west  and  east  of  the  main 
tunnel.  The  hanging  wall  is  diabase,  dipping  24°  N.  25°  W. 

Operations  at  the  Porter  mine  were  begun  in  1855.  In  1875  the 
excavation  was  reported  to  be  about  40  feet  deep  and  14  feet  below 
the  water  in  Yellow  Breeches  Creek.  Ore  was  loaded  from  the  pit 
into  carts.  The  ore  bed  is  said  to  have  been  from  3 to  6 feet  thick,  to 
have  been  opened  for  25  feet  along  the  strike,  and  to  have  dipped  30° 
toward  the  creek. 

At  the  Shelley  mine  20  feet  of  diabase  is  reported  above  the  ore. 
The  ore  bed  was  10  feet  thick  and  rested  upon  “ Potomac  marble  ” — 
that  is,  upon  limestone  conglomerate. 

“ Second  Geol.  Survey  Pennsylvania,  Rept.  CC,  1877,  pp.  220-222. 

54370— Bull.  359—08 7 


98 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


Frazer  regarded  the  inclosing  rock  of  the  Porter  ore  as  probably 
Paleozoic  limestone.  Though  the  rock  exposed  in  the  near-by  cut- 
ting along  the  railroad  was  thought  by  him  to  be  “Auroral  lime- 
stone,” the  present  writer  is  confident  that  it  is  limestone  conglomer- 
ate belonging  to  the  Mesozoic  belt.  These  strata  dip  toward  the 
south  at  a loiv  angle.  A thin  sill  of  diabase  is  seen  in  contact  with 
the  calcareous  rock,  which  is  considerably  metamorphosed. 

The  following  notes  are  given  by  D’lnvilliers : ° 

The  old  Fuller  or  Landis  mine  is  owned  and  worked  by  Mr. 
Shelley,  who  states  that  a shaft  80  feet  deep  passed  through  diabase 
to  a chimney-shaped  bed  of  ore  dipping  north-northeast.  The  same 
ore  was  struck  100  feet  farther  east  by*  a 40-foot  shaft,  in  which  the 
ore  also  dips  toward  the  creek.  According  to  Mr.  Shelley,  there  are 
four  or  five  beds  here,  separated  by  short  intervals  of  hard  rock  of  a 
white  color,  and  not  unlike  a baked  slaty  sandstone.  In  April,  1887, 
preparations  were  being  made  to  sink  on  the  outcrop  of  a lower  bed 
showing  about  100  yards  south  of  the  shaft.  , 

Immediately  across  a narrow  ravine  to  the  east  of  this  opening  a 
large  amount  of  ore  was  formerly  raised  b}^  Mr.  Fuller,  and  the 
operation  is  supposed  to  have  been  stopped  owing  to  the  occurrence 
of  “ Potomac  marble,”  which  cuts  out  the  ore  for  a considerable  ex- 
tent through  the  mine  and  along  the  railroad.  This  rock  shows 
largely  through  the  field  and  along  the  track,  where  , an  abandoned 
cut  developed  a large  body  of  soft  surface  ore,  resulting  from  the  de- 
composition of  the  bed,  5 to  8 feet  thick,  which  wTas  encountered  in 
the  bottom  of  the  pit.  Mr.  Shelley  says  that  there  are  13  acres  in 
this  property  through  which  no  pinching  in  the  ore  beds  occurs,  so 
far  as  developed. 

MINES  SOUTHWEST  OF  WELLSVILLE. 

The  so-called  “ Minebank  ” workings  are  situated  about  2 miles 
southwest  of  Wellsville,  and  about  miles  from  the  northwest 
boundary  of  the  Mesozoic  belt  (PI.  XIX).  The  most  prominent 
feature  in  the  local  geology  is  a mass  of  intrusive  diabase,  which 
appears  at  the  surface  in  an  elliptical  area  about  24  miles  long  and 
1 mile  wide.  This  diabase  is  surrounded  by  shales  and  sandstones 
which  are  bleached  and  baked  in  the  vicinity  of  the  igneous  rock. 
The  general  strike  of  the  strata  is  northeast  and  southwest,  and  dips, 
wherever  observable,  are  toward  the  northwest,  usually  at  moderate 
angles. 

The  u Minebank  ” deposit  appears  to  be  a layer  conforming  to  the 
strata  by  which  it  is  inclosed.  It  has  been  opened  by  a series  of  pits 
and  shafts  extending  from  southwest  to  northeast  for  a distance  of 
about  1,000  feet  along  the  strike  of  the  outcrop,  and  indications  of 


n Ann.  Kept.  (Jcol.  Survey  Pennsylvania  for  1886,  pt.  4,  1887,  pp.  1513—1514. 


YORK  COUNTY  DEPOSITS. 


99 


ore  were  found  in  explorations  beyond  the  northeasternmost  and 
largest  mine,  which  is  situated  back  of  the  schoolhouse.  Although  a 
narrow  dike  of  diabase  is  said  to  have  been  encountered  in  one  of  the 
mines,  the  main  intrusion  lies  some  distance  northwest  of  the  ore 
cropping.  The  dip  of  the  strata  which  inclose  the  ore  is  toward  the 
diabase.  The  waste  to  be  seen  on  the  mine  dump  consists  mainly  of 
baked  shale  and  fine-grained  sandstone.  Specimens  may  be  seen  in 
which  joints  crossing  the  stratification  contain  films  of  micaceous 
hematite.  Lumps  of  solid,  ore  may  be  found  composed  either  of 
hematite  and  magnetite  together,  or  of  hematite  alone.  Some  of  the 
micaceous  ore,  which  looks  like  specular  hematite,  yields  a black 
powder  instead  of  the  red  powder,  which  is  characteristic  of  hematite, 
and  is  attracted  by  the  magnet.  A mass  of  similar  ore  is  reported  to 
have  been  mined  out  years  ago  from  one  of  the  Phoenix  mines  at 
Boyertown.  Several  blocks  were  noted  which  were  composed  of  crys- 
talline limestone  and  specular  hematite  with  a sprinkling  of  chal- 
copyrite.  A stud}7  of  this  material  leaves  little  doubt  that  the  iron 
mineral  has  been  deposited  through  some  process  of  chemical  substi- 
tution. From  the  presence  of  the  limestone  it  may  be  thought  that 
the  ore  layer  was  formed  by  the  replacement  of  a limestone  stratum 
interbedded  with  the  shales  and  sandstones  which  are  the  common 
rocks  of  the  region.  Whether  this  be  true  or  not,  there  can  be  little 
doubt  that  the  ore  was  introduced  through  the  agency  of  hot  water 
or  gases,  impelled  by  the  adjacent  intrusive  mass  of  diabase.  From 
the  description  given  below  it  appears  that  the  mineralizing  solutions 
followed  the  narrowT  dike  or  sill  of  diabase  which  was  encountered 
in  the  mine.  Though  showings  of  ore  have  been  reported  at  several 
places  in  the  vicinity  of  the  large  diabase  mass,  no  minable  body  of 
ore  has  been  discovered  aside  from  the  one  at  Minebank.® 

The  following  data  are  abstracted  from  Frazer’s  report:* 6 
Ore  was  first  discovered  in  the  vicinity  of  the  present  workings 
about  1805.  Prospecting  in  1872  led  to  the  opening  of  the  Altland 
shaft,  which  passes  through  5 feet  of  soil,  then  25  feet  of  light- 
greenish  hard  sandstone,  below  which  a 6-foot  bed  of  micaceous  ore 
was  encountered.  Beneath  the  ore  was  blue  to  gray  sandstone,  sim- 
ilar to  that  above  except  for  being  harder.  The  ore  was  followed  by 
a slope  until  a diabase  dike  was  encountered.  The  dip  measured  on 
the  sandstone  is  31°  to  35°  N.  30°  W.  A second  shaft  was  sunk  in 
the  same  year,  about  120  feet  north  of  the  first.  In  1875  the  gang- 
ways along  the  ore  had  a total  length  of  about  500  feet.  The  ore  lies 
between  the  sandstone  in  regular  layers,  varying  from  6 inches  to 
7 feet  in  thickness,  with  occasional  sandstone  partings.  It  is  in  many 
places  found  cutting  into  the  diabase.  The  boundary  between  the 
latter  and  the  sandstone  is  very  clearly  defined.  Ore  had  been  found 

0 Second  Geol.  Survey  Pennsylvania,  Kept.  CC,  1877,  pp.  231-238. 

6 Op.  cit.,  pp.  235-236. 


100 


MAGNETITE  DEPOSITS  IN  PENNSYLVANIA. 


on  the  northwest  side  of  the  dike,  but  up  to  1875  not  in  paying  quan- 
tities. Sixty  feet  doAvn  the  slope  and  50  feet  northwest  of  it  both 
the  sandstone  and  the  diabase  dip  30°  NW.  The  diabase  is  here  4 
feet  thick.  Thirty  feet  north  of  the  shaft,  2 or  3 yards  of  rock  in 
contact  with  the  dike  showed  no  ore,  but  the  vein  had  been  proved 
from  this  point  to  the  surface.  The  ore  is  very  micaceous. 

BENDER  MINE. 

Near  the  York  Springs  road,  about  a mile  southwest  of  Dillsburg, 
are  two  old  pits  from  which  iron  ore  was  formerly  extracted.  One  of 
these  is  situated  east  of  the  road,  very  near  the  boundary  of  the  in- 
trusive diabase,  at  the  south  end  of  an  embayment  of  sedimentary 
rocks.  No  exposures  of  rock  in  place  are  to  be  seen  near  this  open- 
ing, but  limestone  conglomerate  and  red  sandy  shale  occur  in  the 
quarry  beside  the  road  less  than  one-fourth  mile  to  the  north.  The 
mine  is  reported  to  have  been  a small  one.  The  second  mine,  known 
as  the  Bender  property,  is  located  about  one-fourth  mile  farther 
southwest,  on  the  west  side  of  the  wagon  road.  This  deposit  is  said 
to  have  been  opened  in  1849,  in  which  year  200  tons  of  ore  was  ex- 
tracted. In  1873  about  80  tons  of  ore  was  mined  from  a so-called 
pocket  averaging  5 feet  thick,  lying  under  7 feet  of  stripping.  The 
mine  was  worked  entirely  by  open  pit.® 

In  the  neighborhood  of  the  Bender  pit  irregularly  shaped  masses 
of  extremely  hard  and  dense  green  rock  may  be  found  lying  upon 
* the  surface  or  embedded  in  the  soil.  This  flinty  material  is  a much 
baked  sedimentary  rock,  probably  a limy  shale  or  impure  limestone 
in  its  original  state.  Some  of  the  specimens  examined  are  composed 
almost  entirely  of  massive  garnet;  others  contain  considerable  col- 
orless p}rroxene.  Bowlders  of  this  rock  may  be  found  in  an  area 
300  to  400  feet  long  and  about  100  feet  wide.  Soil  derived  from  dia- 
base is  present  on  all  sides  of  this  patch,  so  that  the  strata  with  which 
the  ore  is  associated  evidently  form  an  isolated  mass,  surrounded  by 
the  intrusive  rock.  The  locality  is  near  the  west  side  of  the  diabase 
intrusion,  here  about  one-half  mile  wide,  which  runs  northeastward 
to  Dillsburg  and  thence  southeastward  and  eastward  to  join  the  great 
mass  which  forms  the  group  of  high  hills  between  Stevenstown  and 
Mount  Airy.  Southwest  of  Dillsburg  this  band  of  diabase  has  been 
followed  for  about  8 miles. 

Flinty  rock  like  that  described  above  occurs  on  the  east  side  of  the 
diabase  about  a mile  south  of  the  Bender  pit,  but  in  this  vicinity  indi- 
cations of  ore  are  not  known  to  have  been  found.  From  the  occur- 
rence of  limestone  conglomerate  in  the  valley  west  of  the  Bender  mine 
it  seems  possible  that  a bed  of  this  rock  may  have  been  replaced  in 
the  formation  of  the  ore  deposit. 


" Second  Geol.  Survey  Pennsylvania',  Rept.  CC,  1877,  p.  226. 


INDEX. 


Page. 

Altland  mine,  description  of ' 81-82 

Basalt,  flows  of 9 

Bell  mine,  description  of 78-79 

plan  and  sections  of,  figures  showing 78,79 

Bender  mine,  description  of ICO 

Berks  County,  ores  of 12,29-71 

ores  of,  analyses  of. . . 11 

Black  vein,  relations  of,  figure  showing CO 

See  also  Warwick  mine. 

Blue  vein,  location  of 43,55 

Boyertown,  fault  near 58 

fault  near,  position  of,  plate-  showing 56 

geologic  map  of 44 

geology  near 44-46 

maps  near 44,61,C3 

mines  of,  sections  of,  plate  showing 46 

workings  of, plate  showing  46,48,50,52,54,56 

ore  deposits  of 12,43-C1 

ore  deposits  near C1-C5 

prospecting  near 57-C1 

Brower  mine,  description  of C2 

California  mine,  description  of 47-48,50-51,56-58 

plan  of,  plate  showing 56 

Cambrian  quartzites,  occurrence  and  character 

of 8 

Cambro-Ordovician  limestones,  occurrence 

and  character  of 8 

Casper  mine,  ores  of 28-29 

Chester  County,  ores  of 12 

Cobalt,  occurrence  of 11 

Conglomerate,  occurrence  and  character  cf.  18, 43,73 

Congo,  copper  near C5 

Cornwall,  mines  near,  geologic  map  cf 20 

ore  deposits  at 17-28 

distribution  of 17-19 

erosion  of 21 

extent  of 21-28 


intrusions  in 19 


structure  of 20-21 

surface  relations  of 17-18 

See  also  Cornwall  ore  body. 

ore  deposits  near 23-29 

ores  of 11 

analyses  of 11 

Cornwall  district,  geologic  map  of 18 

ores  of 17-29 

structure  sections  of,  plate  showing 20 

See  also  Cornwall. 

Cornwall  ore  body,  description  of 22-23 

Cox  mine,  description  of 76-77 

Diabase,  intrusions  of 9-10,  passim 

intrusions  of,  map  showing 8 

relation  of,  to  ores 10, 12, 16,  passim 


Page. 

Dikes,  occurrence  and  character  cf 9-10 

Dillsburg,  geologic  map  near 72, 74 

mines  near 71-75 

description  cf 75-92 

diabase  near 92-93 

map  of 74 

ores  of 11,12 

conclusions  on 93-96 

D’Invilliers,  E.  V.,  on  Altland  mine 81-82 

on  Bell  mine 78 

on  Boyertown  mines 49-55 

on  Cox  mines 76-77 

on  Grantham  mines 98 

on  Island  mine 38, 40 

on  Randenbusch  mine 36 

on  Underwood  workings 85 

Drill  holes,  records  of 24 

East  vein,  .location  of 43 

structure  near,  map  showing 59 

workings  on 43 

Eckert  vein,  location  of 43 

workings  on 43,47-49 

Esterly  mine,  description  of 41-43 

Faulting.  See  Folding  and  faulting. 

Fegley  mine,  ore  from 64-65 

Folding  and  faulting,  prevalence  of 8 

Frazer,  Persiflor,  on  Bell  mine 79 

on  Grantham  mines • 97 

on  Jones  mine  vicinity 68-69 

on  McCormick  mines 88-92 

on  Minnebank  mine 99-100 

on  Underwood  workings 84 

Fritz  Island,  geologic  map  of 38 

ore  deposits  on  and  near 38-41 

sections  on,  figures  showing 39 

Fritztown  station,  geology  near 36 

Fuller  mine.  See  Landis  mine. 

Gabel  mine,  description  of 47,53-56 

geology  of 45 

plan  of,  plate  showing 44 

section  of 53 

figure  showing 60 

Geology,  description  of 7-10 

Gilbert  shaft,  ore  from 63 

Grantham  mines,  description  of 72,96-98 

Grove  mine,  description  of 77 

Hagy  vein,  location  of 43, 57-59 

structure  near,  map  showing 59 

workings  on 43 

Harden,  J.  H.,  map  by 47 

Hummelstown,  ores  near 29 

Igneous  rocks,  occurrence  and  character  of. . . 9-10 
Iron,  source  of 13-16 


101 


102 


INDEX. 


Page. 

Island  mine,  description  of 38-40 

Jauss  mine,  description  of 79-81 

plan  of,  figure  showing 79 

section  of,  figure  showing 80 

Joanna  station,  ores  near 12 

Jones  mine,  description  of 65-69 

geologic  map  of 66 

map  of 68 

sections  of,  figures  showing 66,67 

King  mine,  description  of 79-81 

Kinney  mine,  geology  of 66-68 

map  of 66 

section  of,  figure  showing 66-67 

Knauertown,  ores  near 71 

Lancaster  County,  geology  in 20 

Landis  mine,  description  of 96-98 

Lebanon,  ore  deposits  near.  See  Cornwall. 

Lewis,  J.  V.,  on  New  Jersey  copper 65 

Logan  mine,  description  of 75-76 

Longnecker  mine,  description  of 83-88 

sections  of,  figures  showing V.  85, 87 

McCormick  mines,  description  of 88-92 

map  of,  figure  showing 90 

sections  in 88-99,91 

McCreath,  A.  S.,  analyses  by 11 

Mesozoic  rocks,  occurrence  and  character  of.  8-9 

occurrence  and  character  of,  map  showing.  8, 74 

Metamorphism,  occurrence  and  character  of.  14-16 

relation  of,  to  ores 13,15-16 

Mill  Ridge,  geology  of 26 

Minnebank,  ore  deposits  near 71-72,98-100 

Newark  group.  See  Mesozoic  rocks. 

Nova  Scotia,  ores  of 12 

Ordovician  shales,  occurrence  and  character  of  8 

Ore  deposits,  occurrence  and  character  of.  10, 16-17 

ores  of.  See  Ores. 

Ores,  analyses  of 11 

composition  of ’. 11 

distribution  of .• . . 12 

geologic  relations  of 12 

metamorphism  of .’ 16 

origin  of 13-16 

See  also  particular  mines. 

Paleozoic  rocks,  occurrence  and  character  of.  8 

Peckitt,  Leonard,  analyses  by 11 

Phoenix  mines,  description  of 47-51 

Porter  mine,  description  of 96-97 

Price  farm,  prospects  on 77-78 

Price  mine,  description  of. 77 


Page. 

Pyrite,  occurrence  of 10 

Raudenbusch  mine,  description  of 36-37 

Reading,  geologic  map  near 30 

ores  near 12 

Replacement  deposits,  occurrence  and  char- 
acter of 13 

Reservoir,  ores  near 23-24 

Rhoades  and  Ginn  shaft,  description  of 62 

Rhoades  vein,  location  of 43, 47 

workings  on 44, 47 

Richards,  Richard,  on  Boyertown  mines 57,62 

Rogerg,  H.  D.,  on  Jones  mine 66 

on  Raudenbusch  mine. 36 

on  Yfarwick  mine. C9-70 

Rowe,  W.  G.,  on  Esterly  mine 41,42 

Ruth  mine,  section  at,  figure  showing 31 

Schuylkill  River,  ore  deposits  on 40-41 

Scope  of  paper 7 

Second  Geological  Survey  of  Pennsylvania, 

on  Paleozoic  rocks 8 

Sedimentary  rocks,  description  of 8-9 

Shale,  occurrence  and  character  of 45-46 

Shelley  mine,  description  of 93-98 

Smyser  mine,  description  of 82-83 

South  Mountain,  geology  at 73-74 

Underwood  workings,  description  of 83-86 

section  of,  figure  showing . . .*. 85 

Warwick  mine  (Berks  Co.),  description  of 43- 

45,48-49,51-53,56 

map  of,  figure  showing 48 

plan  of,  plate  showing 56 

vein  of,  location  of. 43, 57 

Warwick  mine  (Chester  Co.),  description  of. . 69-71 

geologic  map  of 66 

section  of,  figure  showing 69 

Wells ville,  mines  near. i . . . 98-100 

Wheatfield  group,  description  of 29-30 

diabase  and,  relation  of 30 

geologic  map  of 32 

ore  deposits  of,  distribution  of 34-36 

ores  of,  character  of 31, 35 

structure  at 31-34 

figure  showing 31,32,33 

Willis,  Bailey,  on  Boyertown  mines 47-49 

York  County,  mines  of,  description  of 74-100 

ore  deposits  in 71-100 

ores  from * 12 

analyses  of 11 


o 


